_section: Migrating from v5 @<migrating> @priority<-10>

This guide aims to capture some of the high-level differences
between v5 and v6 to help those migrating an existing app and
those already familiar with v5 that just need a quick primer.

The biggest differnce in v6 is the use of modern ES6 features,
so a lot of changes are largely internal.

- [BigNumbers](migrate-bigint)
- [Contracts](migrate-contracts)
- [Importing](migrate-importing)
- [Odds and Ends](migrate-other)


_subsection: Big Numbers  @<migrate-bigint>

One of the biggest changes in v6 is that the //BigNumber// class has
been replaced with the built-in ES2020 BigInt offered by modern
JavaScript environments.

There is plenty of [online documentation](link-js-bigint) to get
you started with JavaScript ES2020 BigInt. Keep in mind, just like
//BigNumber//, a ES2020 BigInt can **only** operate on integers.

The [[FixedNumber]] class still exists for performing fixed-point
maths.


_code: creating large numbers  @lang<script>

  // Using BigNumber in v5
  value = BigNumber.from("1000")

  // Using BigInt in v6 (ysing literal notation).
  // Notice the suffix n
  value = 1000n

  // Using the BigInt function for strings
  value = BigInt("1000")


_code: simple maths on large numbers  @lang<script>

  // Adding two values in v5
  sum = value1.add(value2)

  // Using BigInt in v6; keep in mind, both values
  // must be a BigInt
  sum = value1 + value2


_code: simple comparison on large numbers  @lang<script>

  // Checking equality in v5
  isEqual = value1.eq(value2)

  // Using BigInt in v6
  isEqaul = (value1 == value2)


_subsection: Contracts @<migrate-contracts>

The [[Contract]] is an ES6 Proxy, which means it can resolve
method names at run-time.

_heading: Ambiguous Methods

In v5, in the case of an ambiguous method, it was necessary to
look up a method by its canonical normalized signature. In v6
the signature does not need to be normalized and the Typed API
provides a cleaner way to access the desired method.

In v5, duplicate definitions also injected warnings into the
console, since there was no way to detect them at run-time.

_code: contracts in v5 @lang<script>
  abi = [
    "function foo(address bar)",
    "function foo(uint160 bar)",
  ]
  contract = new Contract(address, abi, provider)

  // In v5 it was necessary to specify the fully-qualified normalized
  // signature to access the desired method. For example:
  contract["foo(address)"](addr)

  // These would fail, since there signature is not normalized:
  contract["foo(address )"](addr)
  contract["foo(address addr)"](addr)

  // This would fail, since the method is ambiguous:
  contract.foo(addr)

_code: contracts in v6  @lang<script>
  abi = [
    "function foo(address bar)",
    "function foo(uint160 bar)",
  ]
  contract = new Contract(address, abi, provider)

  // Any of these work fine:
  contract["foo(address)"](addr)
  contract["foo(address )"](addr)
  contract["foo(address addr)"](addr)

  // This still fails, since there is no way to know which
  // method was intended
  contract.foo(addr)

  // However, the Typed API makes things a bit easier, since it
  // allows providing typing information to the Contract:
  contract.foo(Typed.address(addr))

_heading: Other Method Operations

In v5, contracts contained a series of method buckets, which
then in turn had all signatures and non-ambiguous names
attached to them to perform less-common operations.

In v6, the methods each have their own less-common operations
attached directly to them.

_code: other operations in v5  @lang<script>

  // The default action chooses send or call base on method
  // type (pure, view, constant, non-payable or payable)
  contract.foo(addr)

  // This would perform the default action, but return a Result
  // object, instead of destructing the value
  contract.functions.foo(addr)

  // Forces using call
  contract.staticCall.foo(addr)

  // Estimate the gas
  contract.estimateGas.foo(addr)

  // Populate a transaction
  contract.populateTransaction.foo(addr)

_code: other operations in v6  @lang<script>

  // Still behaves the same
  contract.foo(addr)

  // Perform a call, returning a Result object directly
  contract.foo.staticCallResult(addr)

  // Forces using call (even for payable and non-payable)
  contract.foo.staticCall(addr)

  // Forces sending a transaction (even for pure and view)
  contract.foo.send(addr)

  // Estimate the gas
  contract.foo.estimateGas(addr)

  // Populate a transaction
  contract.foo.populateTransaction(addr)


_subsection: Importing  @<migrate-importing>

In v5, the project was maintained as a large set of sub-packages
managed as a monorepo.

In v6 all imports are available in the root package, and for those
who wish to have finer-grained control, the ``pkg.exports`` makes
certain folders avilable directly.

_code: importing in v5  @lang<script>

  // Many things (but not all) we available on the root package
  import { ethers } from "ethers"

  // But some packages were grouped behind an additional property
  import { providers } from "ethers"
  const { InfuraProvider } = providers

  // For granular control, importing from the sub-package
  // was necessary
  import { InfuraProvider } from "@ethersproject/providers"

_code: importing in v6  @lang<script>

  // Everything is available on the root package
  import { ethers } from "ethers"
  import { InfuraProvider } from "ethers"

  // The pkg.exports provides granular access
  import { InfuraProvider } from "ethers/providers"


_subsection: Odds and Ends @<migrate-other>


_code: default AbiCoder  @lang<script>
  // In v5, it is a property of AbiCoder
  coder = AbiCoder.defaultAbiCoder

  // In v6, it is a static function on AbiCoder, which uses
  // a singleton pattern; the first time it is called, the
  // AbiCoder is created and on subsequent calls that initial
  // instance is returned.
  coder = AbiCoder.defaultAbiCoder()