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<li class="toctree-l3"><a class="reference internal" href="#connecting-to-a-contract">Connecting to a Contract</a></li>
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<div class="section" id="contracts">
<span id="api-contract"></span><h1>Contracts<a class="headerlink" href="#contracts" title="Permalink to this headline"></a></h1>
<p>This API provides a graceful connection to a contract deployed on the blockchain,
simplifying calling and querying its functions and handling all the binary
protocol and conversion as necessarily.</p>
<p>The Contract object is a meta-class, so many of the functions it will have are
not defined until it is instantiated with an application binary interface (ABI)
which is usually generated by a compiler, such as Solidity.</p>
<p>To better see this demonstrated, see the <a class="reference internal" href="#example">example</a> below.</p>
<div class="highlight-default"><div class="highlight"><pre><span></span><span class="n">var</span> <span class="n">Contract</span> <span class="o">=</span> <span class="n">ethers</span><span class="o">.</span><span class="n">Contract</span><span class="p">;</span>
</pre></div>
</div>
<hr class="docutils" />
<div class="section" id="connecting-to-a-contract">
<h2>Connecting to a Contract<a class="headerlink" href="#connecting-to-a-contract" title="Permalink to this headline"></a></h2>
<dl class="docutils">
<dt>new <sup>ethers</sup> . Contract ( addressOrName , interface , providerOrSigner )</dt>
<dd><p class="first">Connects to the contract at <em>addressOrName</em> defined by <em>interface</em>, which
may be a JSON string or the parsed object.</p>
<p>The <em>providerOrSigner</em> may be any instance of the following:</p>
<dl class="last docutils">
<dt><a class="reference internal" href="api-wallet.html#api-wallet"><span class="std std-ref">Wallet</span></a></dt>
<dd>The wallet will be used to sign and send transactions, and
estimates and calls will use the wallet address.</dd>
<dt><a class="reference internal" href="api-providers.html#api-provider"><span class="std std-ref">Provider</span></a></dt>
<dd>Gas estimates and constant functions can be called (but without an
address) and event callbacks may be registered.</dd>
<dt><a class="reference internal" href="#id2">Custom Signer</a></dt>
<dd>For much more control over how and when signing and sending
transaction occurs and to defer address behaviour.</dd>
</dl>
</dd>
</dl>
</div>
<hr class="docutils" />
<div class="section" id="prototype">
<h2>Prototype<a class="headerlink" href="#prototype" title="Permalink to this headline"></a></h2>
<p>The prototype will contain all the methods and events defined in the
<strong>interface</strong>.</p>
<p>The result of all contant methods are a <a class="reference internal" href="notes.html#promise"><span class="std std-ref">Promise</span></a> which
resolve to the result as a tuple, optionally with the parameters
accessible by name, if named in the ABI.</p>
<p>The result of all non-constant methods are a <a class="reference internal" href="notes.html#promise"><span class="std std-ref">Promise</span></a>
which resolve to the <a class="reference internal" href="api-providers.html#transactionrequest"><span class="std std-ref">transaction</span></a> that
was sent to the network.</p>
<p>Name collisions with the built-in properties (below) will not be overwritten.
Instead, they must be accessed through the <strong>functions</strong> or <strong>events</strong>
property.</p>
<p>Due to signature overloading, multiple functions can have the same name. The
first function specifed in the ABI will be bound to its name. To access
overloaded functions, use the full typed signature of the functions (e.g.
<code class="docutils literal"><span class="pre">contract[&quot;foobar(address,uint256)&quot;]</span></code>).</p>
<dl class="docutils">
<dt><sup>prototype</sup> . address</dt>
<dd>The address (or ENS name) of the contract.</dd>
<dt><sup>prototype</sup> . interface</dt>
<dd>The <a class="reference internal" href="api-advanced.html#api-interface"><span class="std std-ref">Interface</span></a> meta-class of the parsed
ABI. Generally, this should not need to be accessed directly.</dd>
<dt><sup>prototype</sup> . functions . <em>functionName</em></dt>
<dd>An object that maps each ABI function name to a function that will
either call (for contant functions) or sign and send a transaction
(for non-constant functions)</dd>
<dt><sup>prototype</sup> . estimate . <em>functionName</em></dt>
<dd>An object that maps each ABI function name to a function that will
estimate the cost the provided parameters.</dd>
<dt><sup>prototype</sup> . events . on<em>eventname</em></dt>
<dd>An object that maps each ABI event name (lower case, with the “on”
prefix) to a callback that is triggered when the event occurs.</dd>
<dt><sup>prototype</sup> . connect ( providerOrSigner )</dt>
<dd>Create a new instance of the Contract connected as the new <em>providerOrSigner</em>.</dd>
</dl>
<div class="section" id="examples">
<span id="example"></span><h3>Examples<a class="headerlink" href="#examples" title="Permalink to this headline"></a></h3>
<p><em>Example Contract and Interface</em></p>
<div class="highlight-default"><div class="highlight"><pre><span></span><span class="o">/**</span>
<span class="o">*</span> <span class="n">contract</span> <span class="n">SimpleStore</span> <span class="p">{</span>
<span class="o">*</span>
<span class="o">*</span> <span class="n">event</span> <span class="n">valueChanged</span><span class="p">(</span><span class="n">address</span> <span class="n">author</span><span class="p">,</span> <span class="n">string</span> <span class="n">oldValue</span><span class="p">,</span> <span class="n">string</span> <span class="n">newValue</span><span class="p">);</span>
<span class="o">*</span>
<span class="o">*</span> <span class="n">address</span> <span class="n">_author</span><span class="p">;</span>
<span class="o">*</span> <span class="n">string</span> <span class="n">_value</span><span class="p">;</span>
<span class="o">*</span>
<span class="o">*</span> <span class="n">function</span> <span class="n">setValue</span><span class="p">(</span><span class="n">string</span> <span class="n">value</span><span class="p">)</span> <span class="n">public</span> <span class="p">{</span>
<span class="o">*</span> <span class="n">_author</span> <span class="o">=</span> <span class="n">msg</span><span class="o">.</span><span class="n">sender</span><span class="p">;</span>
<span class="o">*</span> <span class="n">valueChanged</span><span class="p">(</span><span class="n">_author</span><span class="p">,</span> <span class="n">_value</span><span class="p">,</span> <span class="n">value</span><span class="p">);</span>
<span class="o">*</span> <span class="n">_value</span> <span class="o">=</span> <span class="n">value</span><span class="p">;</span>
<span class="o">*</span> <span class="p">}</span>
<span class="o">*</span>
<span class="o">*</span> <span class="n">function</span> <span class="n">getValue</span><span class="p">()</span> <span class="n">constant</span> <span class="n">public</span> <span class="n">returns</span> <span class="p">(</span><span class="n">string</span> <span class="n">value</span><span class="p">)</span> <span class="p">{</span>
<span class="o">*</span> <span class="k">return</span> <span class="n">_value</span><span class="p">;</span>
<span class="o">*</span> <span class="p">}</span>
<span class="o">*</span>
<span class="o">*</span> <span class="n">function</span> <span class="n">getAuthorAndValue</span><span class="p">()</span> <span class="n">constant</span> <span class="n">public</span> <span class="n">returns</span> <span class="p">(</span><span class="n">address</span> <span class="n">author</span><span class="p">,</span> <span class="n">string</span> <span class="n">value</span><span class="p">)</span> <span class="p">{</span>
<span class="o">*</span> <span class="k">return</span> <span class="p">(</span><span class="n">_author</span><span class="p">,</span> <span class="n">_value</span><span class="p">);</span>
<span class="o">*</span> <span class="p">}</span>
<span class="o">*</span> <span class="p">}</span>
<span class="o">*/</span>
<span class="o">//</span> <span class="n">The</span> <span class="n">interface</span> <span class="kn">from</span> <span class="nn">the</span> <span class="n">Solidity</span> <span class="n">compiler</span>
<span class="n">var</span> <span class="n">ethers</span> <span class="o">=</span> <span class="n">require</span><span class="p">(</span><span class="s1">&#39;ethers&#39;</span><span class="p">);</span>
<span class="n">var</span> <span class="n">abi</span> <span class="o">=</span> <span class="p">[</span>
<span class="p">{</span>
<span class="s2">&quot;constant&quot;</span><span class="p">:</span><span class="n">true</span><span class="p">,</span>
<span class="s2">&quot;inputs&quot;</span><span class="p">:[],</span>
<span class="s2">&quot;name&quot;</span><span class="p">:</span><span class="s2">&quot;getValue&quot;</span><span class="p">,</span>
<span class="s2">&quot;outputs&quot;</span><span class="p">:[{</span><span class="s2">&quot;name&quot;</span><span class="p">:</span><span class="s2">&quot;value&quot;</span><span class="p">,</span><span class="s2">&quot;type&quot;</span><span class="p">:</span><span class="s2">&quot;string&quot;</span><span class="p">}],</span>
<span class="s2">&quot;payable&quot;</span><span class="p">:</span><span class="n">false</span><span class="p">,</span>
<span class="s2">&quot;type&quot;</span><span class="p">:</span><span class="s2">&quot;function&quot;</span>
<span class="p">},</span>
<span class="p">{</span>
<span class="s2">&quot;constant&quot;</span><span class="p">:</span><span class="n">true</span><span class="p">,</span>
<span class="s2">&quot;inputs&quot;</span><span class="p">:[],</span>
<span class="s2">&quot;name&quot;</span><span class="p">:</span><span class="s2">&quot;getAuthorAndValue&quot;</span><span class="p">,</span>
<span class="s2">&quot;outputs&quot;</span><span class="p">:[</span>
<span class="p">{</span><span class="s2">&quot;name&quot;</span><span class="p">:</span><span class="s2">&quot;author&quot;</span><span class="p">,</span><span class="s2">&quot;type&quot;</span><span class="p">:</span><span class="s2">&quot;address&quot;</span><span class="p">},</span>
<span class="p">{</span><span class="s2">&quot;name&quot;</span><span class="p">:</span><span class="s2">&quot;value&quot;</span><span class="p">,</span><span class="s2">&quot;type&quot;</span><span class="p">:</span><span class="s2">&quot;string&quot;</span><span class="p">}</span>
<span class="p">],</span>
<span class="s2">&quot;payable&quot;</span><span class="p">:</span><span class="n">false</span><span class="p">,</span>
<span class="s2">&quot;type&quot;</span><span class="p">:</span><span class="s2">&quot;function&quot;</span>
<span class="p">},</span>
<span class="p">{</span>
<span class="s2">&quot;constant&quot;</span><span class="p">:</span><span class="n">false</span><span class="p">,</span>
<span class="s2">&quot;inputs&quot;</span><span class="p">:[{</span><span class="s2">&quot;name&quot;</span><span class="p">:</span><span class="s2">&quot;value&quot;</span><span class="p">,</span><span class="s2">&quot;type&quot;</span><span class="p">:</span><span class="s2">&quot;string&quot;</span><span class="p">}],</span>
<span class="s2">&quot;name&quot;</span><span class="p">:</span><span class="s2">&quot;setValue&quot;</span><span class="p">,</span>
<span class="s2">&quot;outputs&quot;</span><span class="p">:[],</span>
<span class="s2">&quot;payable&quot;</span><span class="p">:</span><span class="n">false</span><span class="p">,</span>
<span class="s2">&quot;type&quot;</span><span class="p">:</span><span class="s2">&quot;function&quot;</span>
<span class="p">},</span>
<span class="p">{</span>
<span class="s2">&quot;anonymous&quot;</span><span class="p">:</span><span class="n">false</span><span class="p">,</span>
<span class="s2">&quot;inputs&quot;</span><span class="p">:[</span>
<span class="p">{</span><span class="s2">&quot;indexed&quot;</span><span class="p">:</span><span class="n">false</span><span class="p">,</span><span class="s2">&quot;name&quot;</span><span class="p">:</span><span class="s2">&quot;oldValue&quot;</span><span class="p">,</span><span class="s2">&quot;type&quot;</span><span class="p">:</span><span class="s2">&quot;string&quot;</span><span class="p">},</span>
<span class="p">{</span><span class="s2">&quot;indexed&quot;</span><span class="p">:</span><span class="n">false</span><span class="p">,</span><span class="s2">&quot;name&quot;</span><span class="p">:</span><span class="s2">&quot;newValue&quot;</span><span class="p">,</span><span class="s2">&quot;type&quot;</span><span class="p">:</span><span class="s2">&quot;string&quot;</span><span class="p">}</span>
<span class="p">],</span>
<span class="s2">&quot;name&quot;</span><span class="p">:</span><span class="s2">&quot;valueChanged&quot;</span><span class="p">,</span>
<span class="s2">&quot;type&quot;</span><span class="p">:</span><span class="s2">&quot;event&quot;</span>
<span class="p">}</span>
<span class="p">];</span>
<span class="n">var</span> <span class="n">address</span> <span class="o">=</span> <span class="s1">&#39;0x2BA27534A8814765795f1Db8AEa01d5dbe4112d9&#39;</span><span class="p">;</span>
<span class="n">var</span> <span class="n">provider</span> <span class="o">=</span> <span class="n">ethers</span><span class="o">.</span><span class="n">providers</span><span class="o">.</span><span class="n">getDefaultProvider</span><span class="p">(</span><span class="s1">&#39;ropsten&#39;</span><span class="p">);</span>
<span class="n">var</span> <span class="n">contract</span> <span class="o">=</span> <span class="n">new</span> <span class="n">ethers</span><span class="o">.</span><span class="n">Contract</span><span class="p">(</span><span class="n">address</span><span class="p">,</span> <span class="n">abi</span><span class="p">,</span> <span class="n">provider</span><span class="p">);</span>
</pre></div>
</div>
<p><em>Example Constant Function</em> <strong>getAuthorAndValue ( ) returns ( address author , string value )</strong></p>
<div class="highlight-default"><div class="highlight"><pre><span></span><span class="n">var</span> <span class="n">callPromise</span> <span class="o">=</span> <span class="n">contract</span><span class="o">.</span><span class="n">getValue</span><span class="p">();</span>
<span class="n">callPromise</span><span class="o">.</span><span class="n">then</span><span class="p">(</span><span class="n">function</span><span class="p">(</span><span class="n">result</span><span class="p">)</span> <span class="p">{</span>
<span class="n">console</span><span class="o">.</span><span class="n">log</span><span class="p">(</span><span class="s1">&#39;Positional argument [0]; author: &#39;</span> <span class="o">+</span> <span class="n">result</span><span class="p">[</span><span class="mi">0</span><span class="p">]);</span>
<span class="n">console</span><span class="o">.</span><span class="n">log</span><span class="p">(</span><span class="s1">&#39;Positional argument [1]; value: &#39;</span> <span class="o">+</span> <span class="n">result</span><span class="p">[</span><span class="mi">1</span><span class="p">]);</span>
<span class="n">console</span><span class="o">.</span><span class="n">log</span><span class="p">(</span><span class="s1">&#39;Keyword argument [author]; author: &#39;</span> <span class="o">+</span> <span class="n">result</span><span class="o">.</span><span class="n">author</span><span class="p">);</span>
<span class="n">console</span><span class="o">.</span><span class="n">log</span><span class="p">(</span><span class="s1">&#39;Keyword argument [value]; value: &#39;</span> <span class="o">+</span> <span class="n">result</span><span class="o">.</span><span class="n">value</span><span class="p">);</span>
<span class="p">});</span>
<span class="o">//</span> <span class="n">These</span> <span class="n">are</span> <span class="n">identical</span> <span class="n">to</span> <span class="n">the</span> <span class="n">above</span> <span class="n">call</span>
<span class="o">//</span> <span class="n">var</span> <span class="n">callPromise</span> <span class="o">=</span> <span class="n">contract</span><span class="o">.</span><span class="n">functions</span><span class="o">.</span><span class="n">getValue</span><span class="p">();</span>
<span class="o">//</span> <span class="n">var</span> <span class="n">callPromise</span> <span class="o">=</span> <span class="n">contract</span><span class="p">[</span><span class="s1">&#39;getValue()&#39;</span><span class="p">]();</span>
<span class="o">//</span> <span class="n">var</span> <span class="n">callPromise</span> <span class="o">=</span> <span class="n">contract</span><span class="o">.</span><span class="n">functions</span><span class="p">[</span><span class="s1">&#39;getValue()&#39;</span><span class="p">]();</span>
<span class="o">//</span> <span class="n">var</span> <span class="n">callPromise</span> <span class="o">=</span> <span class="n">contract</span><span class="p">[</span><span class="s1">&#39;getValue()&#39;</span><span class="p">]();</span>
</pre></div>
</div>
<p><em>Example Constant Function with Single Return Value</em> <strong>getValue ( ) returns ( string value )</strong></p>
<div class="highlight-default"><div class="highlight"><pre><span></span><span class="n">var</span> <span class="n">callPromise</span> <span class="o">=</span> <span class="n">contract</span><span class="o">.</span><span class="n">getValue</span><span class="p">();</span>
<span class="n">callPromise</span><span class="o">.</span><span class="n">then</span><span class="p">(</span><span class="n">function</span><span class="p">(</span><span class="n">value</span><span class="p">)</span> <span class="p">{</span>
<span class="n">console</span><span class="o">.</span><span class="n">log</span><span class="p">(</span><span class="s1">&#39;Single Return Value:&#39;</span> <span class="o">+</span> <span class="n">value</span><span class="p">);</span>
<span class="p">});</span>
</pre></div>
</div>
<p><em>Example Non-Constant Function</em> <strong>setValue ( string value )</strong></p>
<div class="highlight-default"><div class="highlight"><pre><span></span><span class="o">//</span> <span class="n">to</span> <span class="n">call</span> <span class="n">a</span> <span class="n">non</span><span class="o">-</span><span class="n">constant</span> <span class="n">function</span><span class="p">,</span> <span class="n">the</span> <span class="n">contract</span> <span class="n">needs</span> <span class="n">to</span> <span class="n">be</span>
<span class="o">//</span> <span class="n">initialized</span> <span class="k">with</span> <span class="n">a</span> <span class="n">wallet</span> <span class="ow">or</span> <span class="n">a</span> <span class="n">customSigner</span>
<span class="n">var</span> <span class="n">provider</span> <span class="o">=</span> <span class="n">ethers</span><span class="o">.</span><span class="n">providers</span><span class="o">.</span><span class="n">getDefaultProvider</span><span class="p">(</span><span class="s1">&#39;ropsten&#39;</span><span class="p">);</span>
<span class="n">var</span> <span class="n">address</span> <span class="o">=</span> <span class="s1">&#39;0x2BA27534A8814765795f1Db8AEa01d5dbe4112d9&#39;</span><span class="p">;</span>
<span class="n">var</span> <span class="n">privateKey</span> <span class="o">=</span> <span class="s1">&#39;0x0123456789012345678901234567890123456789012345678901234567890123&#39;</span><span class="p">;</span>
<span class="n">var</span> <span class="n">wallet</span> <span class="o">=</span> <span class="n">new</span> <span class="n">ethers</span><span class="o">.</span><span class="n">Wallet</span><span class="p">(</span><span class="n">privateKey</span><span class="p">,</span> <span class="n">provider</span><span class="p">);</span>
<span class="n">var</span> <span class="n">contract</span> <span class="o">=</span> <span class="n">new</span> <span class="n">ethers</span><span class="o">.</span><span class="n">Contract</span><span class="p">(</span><span class="n">address</span><span class="p">,</span> <span class="n">abi</span><span class="p">,</span> <span class="n">wallet</span><span class="p">);</span>
<span class="n">var</span> <span class="n">sendPromise</span> <span class="o">=</span> <span class="n">contract</span><span class="o">.</span><span class="n">setValue</span><span class="p">(</span><span class="s2">&quot;Hello World&quot;</span><span class="p">);</span>
<span class="n">sendPromise</span><span class="o">.</span><span class="n">then</span><span class="p">(</span><span class="n">function</span><span class="p">(</span><span class="n">transaction</span><span class="p">)</span> <span class="p">{</span>
<span class="n">console</span><span class="o">.</span><span class="n">log</span><span class="p">(</span><span class="n">transaction</span><span class="p">);</span>
<span class="p">});</span>
<span class="o">//</span> <span class="n">This</span> <span class="ow">is</span> <span class="n">identical</span> <span class="n">to</span> <span class="n">the</span> <span class="n">above</span> <span class="n">send</span>
<span class="o">//</span> <span class="n">var</span> <span class="n">sendPromise</span> <span class="o">=</span> <span class="n">contract</span><span class="o">.</span><span class="n">functions</span><span class="o">.</span><span class="n">setValue</span><span class="p">(</span><span class="s2">&quot;Hello World&quot;</span><span class="p">);</span>
<span class="o">//</span> <span class="n">Overriding</span> <span class="n">parameters</span><span class="p">;</span> <span class="nb">any</span> <span class="n">of</span> <span class="n">these</span> <span class="n">are</span> <span class="n">optional</span> <span class="ow">and</span> <span class="n">get</span> <span class="n">passed</span>
<span class="o">//</span> <span class="k">as</span> <span class="n">an</span> <span class="n">additional</span> <span class="n">parameter</span> <span class="n">after</span> <span class="nb">all</span> <span class="n">function</span> <span class="n">parameters</span><span class="o">.</span>
<span class="n">var</span> <span class="n">overrideOptions</span> <span class="o">=</span> <span class="p">{</span>
<span class="n">gasLimit</span><span class="p">:</span> <span class="mi">250000</span><span class="p">,</span>
<span class="n">gasPrice</span><span class="p">:</span> <span class="mi">9000000000</span><span class="p">,</span>
<span class="n">nonce</span><span class="p">:</span> <span class="mi">0</span><span class="p">,</span>
<span class="n">value</span><span class="p">:</span> <span class="n">ethers</span><span class="o">.</span><span class="n">utils</span><span class="o">.</span><span class="n">parseEther</span><span class="p">(</span><span class="s1">&#39;1.0&#39;</span><span class="p">)</span>
<span class="p">};</span>
<span class="n">var</span> <span class="n">sendPromise</span> <span class="o">=</span> <span class="n">contract</span><span class="o">.</span><span class="n">setValue</span><span class="p">(</span><span class="s2">&quot;Hello World&quot;</span><span class="p">,</span> <span class="n">overrideOptions</span><span class="p">);</span>
</pre></div>
</div>
<p><em>Example Event Registration</em> <strong>valueChanged ( author , value )</strong></p>
<div class="highlight-default"><div class="highlight"><pre><span></span><span class="o">//</span> <span class="n">Register</span> <span class="k">for</span> <span class="n">events</span>
<span class="n">contract</span><span class="o">.</span><span class="n">onvaluechanged</span> <span class="o">=</span> <span class="n">function</span><span class="p">(</span><span class="n">oldValue</span><span class="p">,</span> <span class="n">newValue</span><span class="p">)</span> <span class="p">{</span>
<span class="n">console</span><span class="o">.</span><span class="n">log</span><span class="p">(</span><span class="s1">&#39;oldValue: &#39;</span> <span class="o">+</span> <span class="n">oldValue</span><span class="p">);</span>
<span class="n">console</span><span class="o">.</span><span class="n">log</span><span class="p">(</span><span class="s1">&#39;newValue: &#39;</span> <span class="o">+</span> <span class="n">newValue</span><span class="p">);</span>
<span class="p">};</span>
<span class="o">//</span> <span class="n">This</span> <span class="ow">is</span> <span class="n">identical</span> <span class="n">to</span> <span class="n">the</span> <span class="n">above</span> <span class="n">event</span> <span class="n">registry</span>
<span class="o">//</span> <span class="n">contract</span><span class="o">.</span><span class="n">events</span><span class="o">.</span><span class="n">onvaluechanged</span> <span class="o">=</span> <span class="n">function</span><span class="p">(</span><span class="n">author</span><span class="p">,</span> <span class="n">value</span><span class="p">)</span> <span class="p">{</span> <span class="o">...</span>
</pre></div>
</div>
<p><em>Example Non-Constant Gas Estimate</em></p>
<div class="highlight-default"><div class="highlight"><pre><span></span><span class="o">//</span> <span class="n">to</span> <span class="n">get</span> <span class="n">the</span> <span class="n">gas</span> <span class="n">estimate</span><span class="p">,</span> <span class="n">the</span> <span class="n">contract</span> <span class="n">needs</span> <span class="n">to</span> <span class="n">be</span>
<span class="o">//</span> <span class="n">initialized</span> <span class="k">with</span> <span class="n">a</span> <span class="n">wallet</span> <span class="ow">or</span> <span class="n">a</span> <span class="n">customSigner</span>
<span class="n">var</span> <span class="n">provider</span> <span class="o">=</span> <span class="n">ethers</span><span class="o">.</span><span class="n">providers</span><span class="o">.</span><span class="n">getDefaultProvider</span><span class="p">(</span><span class="s1">&#39;ropsten&#39;</span><span class="p">);</span>
<span class="n">var</span> <span class="n">privateKey</span> <span class="o">=</span> <span class="s1">&#39;0x0123456789012345678901234567890123456789012345678901234567890123&#39;</span><span class="p">;</span>
<span class="n">var</span> <span class="n">wallet</span> <span class="o">=</span> <span class="n">new</span> <span class="n">ethers</span><span class="o">.</span><span class="n">Wallet</span><span class="p">(</span><span class="n">privateKey</span><span class="p">,</span> <span class="n">provider</span><span class="p">);</span>
<span class="n">var</span> <span class="n">contract</span> <span class="o">=</span> <span class="n">new</span> <span class="n">ethers</span><span class="o">.</span><span class="n">Contract</span><span class="p">(</span><span class="n">address</span><span class="p">,</span> <span class="n">abi</span><span class="p">,</span> <span class="n">wallet</span><span class="p">);</span>
<span class="n">var</span> <span class="n">estimatePromise</span> <span class="o">=</span> <span class="n">contract</span><span class="o">.</span><span class="n">estimate</span><span class="o">.</span><span class="n">setValue</span><span class="p">(</span><span class="s2">&quot;Hello World&quot;</span><span class="p">);</span>
<span class="n">estimatePromise</span><span class="o">.</span><span class="n">then</span><span class="p">(</span><span class="n">function</span><span class="p">(</span><span class="n">gasCost</span><span class="p">)</span> <span class="p">{</span>
<span class="o">//</span> <span class="n">gasCost</span> <span class="ow">is</span> <span class="n">returned</span> <span class="k">as</span> <span class="n">BigNumber</span>
<span class="n">console</span><span class="o">.</span><span class="n">log</span><span class="p">(</span><span class="s1">&#39;Estimated Gas Cost: &#39;</span> <span class="o">+</span> <span class="n">gasCost</span><span class="o">.</span><span class="n">toString</span><span class="p">());</span>
<span class="p">});</span>
</pre></div>
</div>
</div>
</div>
<hr class="docutils" />
<div class="section" id="result-types">
<h2>Result Types<a class="headerlink" href="#result-types" title="Permalink to this headline"></a></h2>
<p>There are many variable types avaiable in Solidity, some which work well
in JavaScript and others that do not. Here are some note regarding passing
and returning values in Contracts.</p>
<div class="section" id="integers">
<h3>Integers<a class="headerlink" href="#integers" title="Permalink to this headline"></a></h3>
<p>Integers in solidity are a fixed number of bits (aligned to the nearest byte)
and are available in signed and unsigned variants.</p>
<p>For example, a <strong>uint256</strong> is 256 bits (32 bytes) and unsigned. An <strong>int8</strong>
is 8 bits (1 byte) and signed.</p>
<p>When the type is 48 bits (6 bytes) or less, values are returned as a JavaScript
Number, since Javascript Numbers are safe to use up to 53 bits.</p>
<p>Any types with 56 bits (7 bytes) or more will be returned as a BigNumber,
even if the <em>value</em> is within the 53 bit safe range.</p>
<p>When passing numeric values in, JavaScript Numbers, hex strings or any BigNumber
is acceptable (however, take care when using JavaScript Numbers amd performing
mathematic operations on them).</p>
<p>The <strong>uint</strong> and <strong>int</strong> types are aliases for <strong>uint256</strong> and <strong>int256</strong>,
respectively.</p>
</div>
<div class="section" id="strings">
<h3>Strings<a class="headerlink" href="#strings" title="Permalink to this headline"></a></h3>
<p>Strings work fine and require no special care.</p>
<p>To convert between strings and bytes, which may occasionally come up, use the
<a class="reference internal" href="api-utils.html#api-utf8-strings"><span class="std std-ref">utils.toUtf8Bytes()</span></a> and <a class="reference internal" href="api-utils.html#api-utf8-strings"><span class="std std-ref">utils.toUtf8String()</span></a>
utility functions.</p>
</div>
<div class="section" id="bytes">
<h3>Bytes<a class="headerlink" href="#bytes" title="Permalink to this headline"></a></h3>
<p>Bytes are available in fixed-length or dynamic-length variants. In both cases, the
values are returned as a hex string and may be passed in as either a hex string or
as an <a class="reference internal" href="api-utils.html#api-arrayish"><span class="std std-ref">arrayish</span></a>.</p>
<p>To convert the string into an array, use the <a class="reference internal" href="api-utils.html#api-arrayish"><span class="std std-ref">utils.arrayify()</span></a> utility function.</p>
</div>
<div class="section" id="arrays">
<h3>Arrays<a class="headerlink" href="#arrays" title="Permalink to this headline"></a></h3>
<p>Arrays work fine and require no special care.</p>
</div>
</div>
<hr class="docutils" />
<div class="section" id="deploying-a-contract">
<h2>Deploying a Contract<a class="headerlink" href="#deploying-a-contract" title="Permalink to this headline"></a></h2>
<p>To deploy a contract to the Ethereum network, you must have its bytecode
and its application binary interface (ABI), usually generated from the
Solidity compiler.</p>
<dl class="docutils">
<dt><sup>Contract</sup> . getDeployTransaction ( bytecode , interface , … )</dt>
<dd>Generate the transaction needed to deploy the contract specified by
<em>bytecode</em> and <em>interface</em>. Any additional parameters the constructor
take should also be passed in.</dd>
</dl>
<div class="section" id="id1">
<h3><em>Examples</em><a class="headerlink" href="#id1" title="Permalink to this headline"></a></h3>
<div class="highlight-default"><div class="highlight"><pre><span></span><span class="o">/**</span>
<span class="o">*</span> <span class="n">contract</span> <span class="n">Example</span> <span class="p">{</span>
<span class="o">*</span>
<span class="o">*</span> <span class="n">string</span> <span class="n">_value</span><span class="p">;</span>
<span class="o">*</span>
<span class="o">*</span> <span class="o">//</span> <span class="n">Constructor</span>
<span class="o">*</span> <span class="n">function</span> <span class="n">Example</span><span class="p">(</span><span class="n">string</span> <span class="n">value</span><span class="p">)</span> <span class="p">{</span>
<span class="o">*</span> <span class="n">_value</span> <span class="o">=</span> <span class="n">value</span><span class="p">;</span>
<span class="o">*</span> <span class="p">}</span>
<span class="o">*</span> <span class="p">}</span>
<span class="o">*/</span>
<span class="n">var</span> <span class="n">ethers</span> <span class="o">=</span> <span class="n">require</span><span class="p">(</span><span class="s1">&#39;ethers&#39;</span><span class="p">);</span>
<span class="o">//</span> <span class="n">The</span> <span class="n">interface</span> <span class="kn">from</span> <span class="nn">Solidity</span>
<span class="n">var</span> <span class="n">abi</span> <span class="o">=</span> <span class="s1">&#39;[{&quot;inputs&quot;:[{&quot;name&quot;:&quot;value&quot;,&quot;type&quot;:&quot;string&quot;}],&quot;type&quot;:&quot;constructor&quot;}]&#39;</span><span class="p">;</span>
<span class="o">//</span> <span class="n">The</span> <span class="n">bytecode</span> <span class="kn">from</span> <span class="nn">Solidity</span>
<span class="n">var</span> <span class="n">bytecode</span> <span class="o">=</span> <span class="s2">&quot;0x6060604052341561000c57fe5b60405161012d38038061012d83398101604052&quot;</span> <span class="o">+</span>
<span class="s2">&quot;8080518201919050505b806000908051906020019061003f929190610047565b&quot;</span> <span class="o">+</span>
<span class="s2">&quot;505b506100ec565b828054600181600116156101000203166002900490600052&quot;</span> <span class="o">+</span>
<span class="s2">&quot;602060002090601f016020900481019282601f1061008857805160ff19168380&quot;</span> <span class="o">+</span>
<span class="s2">&quot;011785556100b6565b828001600101855582156100b6579182015b8281111561&quot;</span> <span class="o">+</span>
<span class="s2">&quot;00b557825182559160200191906001019061009a565b5b5090506100c3919061&quot;</span> <span class="o">+</span>
<span class="s2">&quot;00c7565b5090565b6100e991905b808211156100e55760008160009055506001&quot;</span> <span class="o">+</span>
<span class="s2">&quot;016100cd565b5090565b90565b6033806100fa6000396000f30060606040525b&quot;</span> <span class="o">+</span>
<span class="s2">&quot;fe00a165627a7a72305820041f440021b887310055b6f4e647c2844f4e1c8cf1&quot;</span> <span class="o">+</span>
<span class="s2">&quot;d8e037c72cd7d0aa671e2f0029&quot;</span><span class="p">;</span>
<span class="o">//</span> <span class="n">Notice</span> <span class="n">we</span> <span class="k">pass</span> <span class="ow">in</span> <span class="s2">&quot;Hello World&quot;</span> <span class="k">as</span> <span class="n">the</span> <span class="n">parameter</span> <span class="n">to</span> <span class="n">the</span> <span class="n">constructor</span>
<span class="n">var</span> <span class="n">deployTransaction</span> <span class="o">=</span> <span class="n">ethers</span><span class="o">.</span><span class="n">Contract</span><span class="o">.</span><span class="n">getDeployTransaction</span><span class="p">(</span><span class="n">bytecode</span><span class="p">,</span> <span class="n">abi</span><span class="p">,</span> <span class="s2">&quot;Hello World&quot;</span><span class="p">);</span>
<span class="n">console</span><span class="o">.</span><span class="n">log</span><span class="p">(</span><span class="n">deployTransaction</span><span class="p">);</span>
<span class="o">//</span> <span class="p">{</span>
<span class="o">//</span> <span class="n">data</span><span class="p">:</span> <span class="s2">&quot;0x6060604052341561000c57fe5b60405161012d38038061012d83398101604052&quot;</span> <span class="o">+</span>
<span class="o">//</span> <span class="s2">&quot;8080518201919050505b806000908051906020019061003f929190610047565b&quot;</span> <span class="o">+</span>
<span class="o">//</span> <span class="s2">&quot;505b506100ec565b828054600181600116156101000203166002900490600052&quot;</span> <span class="o">+</span>
<span class="o">//</span> <span class="s2">&quot;602060002090601f016020900481019282601f1061008857805160ff19168380&quot;</span> <span class="o">+</span>
<span class="o">//</span> <span class="s2">&quot;011785556100b6565b828001600101855582156100b6579182015b8281111561&quot;</span> <span class="o">+</span>
<span class="o">//</span> <span class="s2">&quot;00b557825182559160200191906001019061009a565b5b5090506100c3919061&quot;</span> <span class="o">+</span>
<span class="o">//</span> <span class="s2">&quot;00c7565b5090565b6100e991905b808211156100e55760008160009055506001&quot;</span> <span class="o">+</span>
<span class="o">//</span> <span class="s2">&quot;016100cd565b5090565b90565b6033806100fa6000396000f30060606040525b&quot;</span> <span class="o">+</span>
<span class="o">//</span> <span class="s2">&quot;fe00a165627a7a72305820041f440021b887310055b6f4e647c2844f4e1c8cf1&quot;</span> <span class="o">+</span>
<span class="o">//</span> <span class="s2">&quot;d8e037c72cd7d0aa671e2f002900000000000000000000000000000000000000&quot;</span> <span class="o">+</span>
<span class="o">//</span> <span class="s2">&quot;0000000000000000000000002000000000000000000000000000000000000000&quot;</span> <span class="o">+</span>
<span class="o">//</span> <span class="s2">&quot;0000000000000000000000000b48656c6c6f20576f726c640000000000000000&quot;</span> <span class="o">+</span>
<span class="o">//</span> <span class="s2">&quot;00000000000000000000000000&quot;</span>
<span class="o">//</span> <span class="p">}</span>
<span class="o">//</span> <span class="n">Connect</span> <span class="n">to</span> <span class="n">the</span> <span class="n">network</span>
<span class="n">var</span> <span class="n">provider</span> <span class="o">=</span> <span class="n">ethers</span><span class="o">.</span><span class="n">providers</span><span class="o">.</span><span class="n">getDefaultProvider</span><span class="p">();</span>
<span class="o">//</span> <span class="n">Create</span> <span class="n">a</span> <span class="n">wallet</span> <span class="n">to</span> <span class="n">deploy</span> <span class="n">the</span> <span class="n">contract</span> <span class="k">with</span>
<span class="n">var</span> <span class="n">privateKey</span> <span class="o">=</span> <span class="s1">&#39;0x0123456789012345678901234567890123456789012345678901234567890123&#39;</span><span class="p">;</span>
<span class="n">var</span> <span class="n">wallet</span> <span class="o">=</span> <span class="n">new</span> <span class="n">ethers</span><span class="o">.</span><span class="n">Wallet</span><span class="p">(</span><span class="n">privateKey</span><span class="p">,</span> <span class="n">provider</span><span class="p">);</span>
<span class="o">//</span> <span class="n">Send</span> <span class="n">the</span> <span class="n">transaction</span>
<span class="n">var</span> <span class="n">sendPromise</span> <span class="o">=</span> <span class="n">wallet</span><span class="o">.</span><span class="n">sendTransaction</span><span class="p">(</span><span class="n">deployTransaction</span><span class="p">);</span>
<span class="o">//</span> <span class="n">Get</span> <span class="n">the</span> <span class="n">transaction</span>
<span class="n">sendPromise</span><span class="o">.</span><span class="n">then</span><span class="p">(</span><span class="n">function</span><span class="p">(</span><span class="n">transaction</span><span class="p">)</span> <span class="p">{</span>
<span class="n">console</span><span class="o">.</span><span class="n">log</span><span class="p">(</span><span class="n">transaction</span><span class="p">);</span>
<span class="p">});</span>
</pre></div>
</div>
<hr class="docutils" />
</div>
</div>
<div class="section" id="custom-signer">
<span id="id2"></span><h2>Custom Signer<a class="headerlink" href="#custom-signer" title="Permalink to this headline"></a></h2>
<p>The simplest way to specify a signer is to simply use an instance of a wallet.
However, if more fine-grained control is required, a custom signer allow
deferring the address, signing and sending transactions.</p>
<p>A signer can be any object with:</p>
<dl class="docutils">
<dt><sup>object</sup> . getAddress()</dt>
<dd><p class="first"><em>Required.</em></p>
<p class="last">Which must return a valid address or a <a class="reference internal" href="notes.html#promise"><span class="std std-ref">Promise</span></a> which will resolve to a valid
address or reject an error.</p>
</dd>
<dt><sup>object</sup> . provider</dt>
<dd><p class="first"><em>Required.</em></p>
<p class="last">A provider that will be used to connect to the Ethereum blockchain to issue
calls, listen for events and possibly send transaction.</p>
</dd>
<dt><sup>object</sup> . estimateGas ( transaction )</dt>
<dd><p class="first"><em>Optional.</em></p>
<p>If this is not defined, the provider is queries directly, after populating
the address using <em>getAddress()</em>.</p>
<p class="last">The result must be a <a class="reference internal" href="notes.html#promise"><span class="std std-ref">Promise</span></a> which resolves to the
<a class="reference internal" href="api-utils.html#bignumber"><span class="std std-ref">BigNumber</span></a> estimated gas cost.</p>
</dd>
<dt><sup>object</sup> . sendTransaction ( transaction )</dt>
<dd><p class="first"><em>Optional.</em></p>
<p>If this is defined, it is called instead of sign and is expected to
populate <em>nonce</em>, <em>gasLimit</em> and <em>gasPrice</em>.</p>
<p class="last">The result must be a <a class="reference internal" href="notes.html#promise"><span class="std std-ref">Promise</span></a> which resolves to the sent transaction, or
rejects on failure.</p>
</dd>
<dt><sup>object</sup> . sign ( transaction )</dt>
<dd><p class="first"><em>Optional.</em></p>
<p>If this is defined, it is called to sign a transaction before using the
provider to send it to the network.</p>
<p class="last">The result may be a valid <a class="reference internal" href="api-utils.html#hexstring"><span class="std std-ref">hex string</span></a> or a promise which will resolve to a valid
<a class="reference internal" href="api-utils.html#hexstring"><span class="std std-ref">hex string</span></a> signed transaction or reject on failure.</p>
</dd>
</dl>
<div class="section" id="id3">
<h3><em>Examples</em><a class="headerlink" href="#id3" title="Permalink to this headline"></a></h3>
<div class="highlight-default"><div class="highlight"><pre><span></span><span class="n">var</span> <span class="n">privateKey</span> <span class="o">=</span> <span class="s1">&#39;0x0123456789012345678901234567890123456789012345678901234567890123&#39;</span><span class="p">;</span>
<span class="n">var</span> <span class="n">wallet</span> <span class="o">=</span> <span class="n">new</span> <span class="n">ethers</span><span class="o">.</span><span class="n">Wallet</span><span class="p">(</span><span class="n">privateKey</span><span class="p">);</span>
<span class="n">function</span> <span class="n">getAddress</span><span class="p">()</span> <span class="p">{</span>
<span class="k">return</span> <span class="n">new</span> <span class="n">Promise</span><span class="p">(</span><span class="n">function</span><span class="p">(</span><span class="n">resolve</span><span class="p">,</span> <span class="n">reject</span><span class="p">)</span> <span class="p">{</span>
<span class="o">//</span> <span class="n">Some</span> <span class="n">asynchronous</span> <span class="n">method</span><span class="p">;</span> <span class="n">some</span> <span class="n">examples</span>
<span class="o">//</span> <span class="o">-</span> <span class="n">request</span> <span class="n">which</span> <span class="n">account</span> <span class="kn">from</span> <span class="nn">the</span> <span class="n">user</span>
<span class="o">//</span> <span class="o">-</span> <span class="n">query</span> <span class="n">a</span> <span class="n">database</span>
<span class="o">//</span> <span class="o">-</span> <span class="n">wait</span> <span class="k">for</span> <span class="n">another</span> <span class="n">contract</span> <span class="n">to</span> <span class="n">be</span> <span class="n">mined</span>
<span class="n">var</span> <span class="n">address</span> <span class="o">=</span> <span class="n">wallet</span><span class="o">.</span><span class="n">address</span><span class="p">;</span>
<span class="n">resolve</span><span class="p">(</span><span class="n">address</span><span class="p">);</span>
<span class="p">});</span>
<span class="p">}</span>
<span class="n">function</span> <span class="n">sign</span><span class="p">(</span><span class="n">transaction</span><span class="p">)</span> <span class="p">{</span>
<span class="k">return</span> <span class="n">new</span> <span class="n">Promise</span><span class="p">(</span><span class="n">function</span><span class="p">(</span><span class="n">resolve</span><span class="p">,</span> <span class="n">reject</span><span class="p">)</span> <span class="p">{</span>
<span class="o">//</span> <span class="n">Some</span> <span class="n">asynchronous</span> <span class="n">method</span><span class="p">;</span> <span class="n">some</span> <span class="n">examples</span>
<span class="o">//</span> <span class="o">-</span> <span class="n">prompt</span> <span class="n">the</span> <span class="n">user</span> <span class="n">to</span> <span class="n">confirm</span> <span class="ow">or</span> <span class="n">decline</span>
<span class="o">//</span> <span class="o">-</span> <span class="n">check</span> <span class="n">available</span> <span class="n">funds</span> <span class="ow">and</span> <span class="n">credits</span>
<span class="o">//</span> <span class="o">-</span> <span class="n">request</span> <span class="mi">2</span><span class="n">FA</span> <span class="n">over</span> <span class="n">SMS</span>
<span class="n">var</span> <span class="n">signedTransaction</span> <span class="o">=</span> <span class="n">wallet</span><span class="o">.</span><span class="n">sign</span><span class="p">(</span><span class="n">transaction</span><span class="p">);</span>
<span class="n">resolve</span><span class="p">(</span><span class="n">signedTransaction</span><span class="p">);</span>
<span class="p">});</span>
<span class="p">}</span>
<span class="n">var</span> <span class="n">customSigner</span> <span class="o">=</span> <span class="p">{</span>
<span class="n">getAddress</span><span class="p">:</span> <span class="n">getAddress</span><span class="p">,</span>
<span class="n">provider</span><span class="p">:</span> <span class="n">ethers</span><span class="o">.</span><span class="n">providers</span><span class="o">.</span><span class="n">getDefaultProvider</span><span class="p">(),</span>
<span class="n">sign</span><span class="p">:</span> <span class="n">sign</span>
<span class="p">}</span>
</pre></div>
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