MergeSort in es6!

mergeSort.js

#!/usr/bin/env node
"use strict"
const expect = require('expect.js')

class MergeSort {
  static sort(array) {
    let mid = array.length / 2
    let left = array.slice(0, mid)
    let right = array.slice(mid)

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

    return this.merge(this.sort(left), this.sort(right))
  }

  static merge(left, right) {
    var results = []
    while(left.length || right.length) {
      if (left.length && right.length) {
        if (left[0] < right[0]) {
          results.push(left.shift())
        } else {
          results.push(right.shift())
        }
      } else if (left.length) {
        results.push(left.shift())
      } else if (right.length) {
        results.push(right.shift())
      }
    }
    return results
  }
}

var results = MergeSort.sort([5,7,2,1,3,4,9,10,12,15,11,1,2,3,15,4])
expect(results).to.eql([1, 1, 2, 2, 3, 3, 4, 4, 5, 7, 9, 10, 11, 12, 15, 15])

var results = MergeSort.sort([2,1])
expect(results).to.eql([1,2])