fix trailingComma

.prettierrc

@@ -0,0 +1,7 @@
+{
+  "semi": false,
+  "arrowParens": "always",
+  "singleQuote": true,
+  "printWidth": 110,
+  "trailingComma": "all"
+}

package.json

@@ -1,6 +1,6 @@
 {
   "name": "fixed-merkle-tree",
-  "version": "0.3.4",
+  "version": "0.5.1",
   "description": "Fixed depth merkle tree implementation with sequential inserts",
   "main": "src/merkleTree.js",
   "scripts": {

src/merkleTree.js

@@ -24,7 +24,7 @@ class MerkleTree {
    */
   constructor(levels, elements = [], { hashFunction, zeroElement = DEFAULT_ZERO } = {}) {
     this.levels = levels
-    this.capacity = 1 << levels
+    this.capacity = 2 ** levels
     this.zeroElement = zeroElement
     this._hash = hashFunction || defaultHash
     if (elements.length > this.capacity) {
@@ -47,9 +47,9 @@ class MerkleTree {
       for (let i = 0; i < Math.ceil(this._layers[level - 1].length / 2); i++) {
         this._layers[level][i] = this._hash(
           this._layers[level - 1][i * 2],
-          i * 2 + 1 < this._layers[level - 1].length ?
-            this._layers[level - 1][i * 2 + 1] :
-            this._zeros[level - 1],
+          i * 2 + 1 < this._layers[level - 1].length
+            ? this._layers[level - 1][i * 2 + 1]
+            : this._zeros[level - 1],
         )
       }
     }
@@ -100,9 +100,9 @@ class MerkleTree {
       index >>= 1
       this._layers[level][index] = this._hash(
         this._layers[level - 1][index * 2],
-        index * 2 + 1 < this._layers[level - 1].length ?
-          this._layers[level - 1][index * 2 + 1] :
-          this._zeros[level - 1],
+        index * 2 + 1 < this._layers[level - 1].length
+          ? this._layers[level - 1][index * 2 + 1]
+          : this._zeros[level - 1],
       )
     }
   }
@@ -120,9 +120,8 @@ class MerkleTree {
     const pathIndices = []
     for (let level = 0; level < this.levels; level++) {
       pathIndices[level] = index % 2
-      pathElements[level] = (index ^ 1) < this._layers[level].length ?
-        this._layers[level][index ^ 1] :
-        this._zeros[level]
+      pathElements[level] =
+        (index ^ 1) < this._layers[level].length ? this._layers[level][index ^ 1] : this._zeros[level]
       index >>= 1
     }
     return {
@@ -152,6 +151,36 @@ class MerkleTree {
   elements() {
     return this._layers[0].slice()
   }
+
+  /**
+   * Serialize entire tree state including intermediate layers into a plain object
+   * Deserializing it back will not require to recompute any hashes
+   * Elements are not converted to a plain type, this is responsibility of the caller
+   */
+  serialize() {
+    return {
+      levels: this.levels,
+      _zeros: this._zeros,
+      _layers: this._layers,
+    }
+  }
+
+  /**
+   * Deserialize data into a MerkleTree instance
+   * Make sure to provide the same hashFunction as was used in the source tree,
+   * otherwise the tree state will be invalid
+   *
+   * @param data
+   * @param hashFunction
+   * @returns {MerkleTree}
+   */
+  static deserialize(data, hashFunction) {
+    const instance = Object.assign(Object.create(this.prototype), data)
+    instance._hash = hashFunction || defaultHash
+    instance.capacity = 2 ** instance.levels
+    instance.zeroElement = instance._zeros[0]
+    return instance
+  }
 }
 
 module.exports = MerkleTree

test/merkleTree.test.js

@@ -202,4 +202,19 @@ describe('MerkleTree', () => {
       ])
     })
   })
+
+  describe('#serialize', () => {
+    it('should work', () => {
+      const src = new MerkleTree(10, [1, 2, 3])
+      const data = src.serialize()
+      const dst = MerkleTree.deserialize(data)
+
+      src.root().should.equal(dst.root())
+
+      src.insert(10)
+      dst.insert(10)
+
+      src.root().should.equal(dst.root())
+    })
+  })
 })