Merkle tree written in es6 javascript

merkle.js

#!/usr/bin/env node
"use strict"

const expect = require('expect.js')

class Merkle {
  constructor(array) {
    this.key = array.join('')
    this.left = null
    this.right = null
    this.load(array)
  }

  load(array) {
    if (array.length == 1) return

    var left,
        right,
        mid = Math.floor(array.length / 2)

    if (mid != 1 && mid % 2 != 0) {
      mid += 1
    }

    left = array.slice(0, mid)
    right = array.slice(mid)

    if (left.length) {
      this.left = new Merkle(left)
    }

    if (right.length) {
      this.right = new Merkle(right)
    }
  }
}

// works with 2
var m = new Merkle(['a', 'b'])
expect(m.left.key).to.eql('a')
expect(m.right.key).to.eql('b')

// works with 6
var m = new Merkle(['a', 'b', 'c', 'd', 'e', 'f'])
expect(m.left.key).to.eql('abcd')
expect(m.right.key).to.eql('ef')

// works with 11
var m = new Merkle(['a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k'])
expect(m.left.key).to.eql('abcdef')
expect(m.right.key).to.eql('ghijk')

// works with 12
var m = new Merkle(['a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l'])
expect(m.left.key).to.eql('abcdef')
expect(m.right.key).to.eql('ghijkl')

console.log("All tests pass")