Tree iterators using ES6 generators

binary-tree.js

class BinaryTree {
    constructor(value, left=null, right=null) {
        this.value = value
        this.left = left
        this.right = right
    }
}

inorder-iterator.js

class InOrderIterator extends TreeIterator {
    * [Symbol.iterator] () {
        if (this.tree.left)
            yield* new InOrderIterator(this.tree.left)
        yield this.tree.value
        if (this.tree.right)
            yield* new InOrderIterator(this.tree.right)
    }
}

postorder-iterator.js

class PostOrderIterator extends TreeIterator {
    * [Symbol.iterator] () {
        if (this.tree.left)
            yield* new PostOrderIterator(this.tree.left)
        if (this.tree.right)
            yield* new PostOrderIterator(this.tree.right)
        yield this.tree.value
    }
}

preorder-iterator.js

class PreOrderIterator extends TreeIterator {
    * [Symbol.iterator] () {
        yield this.tree.value
        if (this.tree.left)
            yield* new PreOrderIterator(this.tree.left)
        if (this.tree.right)
            yield* new PreOrderIterator(this.tree.right)
    }
}

test.js

const tree = new BinaryTree('a',
    new BinaryTree('b',
        new BinaryTree('c'),
        new BinaryTree('d')),
    new BinaryTree('e'));

const preOrderIt  = new PreOrderIterator(tree)
const inOrderIt   = new InOrderIterator(tree)
const postOrderIt = new PostOrderIterator(tree)

console.log([...preOrderIt])  // [ 'a', 'b', 'c', 'd', 'e' ]
console.log([...inOrderIt])   // [ 'c', 'b', 'd', 'a', 'e' ]
console.log([...postOrderIt]) // [ 'c', 'd', 'b', 'e', 'a' ]

tree-iteratos.js

class TreeIterator {
    constructor(tree) {
        this.tree = tree
    }

    * [Symbol.iterator] () {
        throw new Error('Not implemented')
    }
}