merge.js

"use strict";

var insertAtRightPlace = function(number, array) {
  var i;

  for(i = 0; i < array.length; i++) {
    if (number <= array[i]) {
      break;
    }
  }

  array.splice(i, 0, number);
};

var merge = function(arrayOfArrays) {
  var i, j, array, newNumber, newArray = [];

  for(i = 0; i < arrayOfArrays.length; i++) {

    array = arrayOfArrays[i];

    for(j = 0; j < array.length; j++) {
      newNumber = array[j];
      insertAtRightPlace(newNumber, newArray);
    }
  }

  return newArray;
};

merge_spec.js

describe('merge', function(){
  it('flattens an array of already sorted arrays and maintains order', function(){
    var arrayOfArrays = [[0, 5, 8, 9], [1, 2, 7], [10]];

    expect(merge(arrayOfArrays)).toEqual([0, 1, 2, 5, 7, 8, 9, 10]);
  });
});

describe('insertAtRightPlace', function(){
  it('takes a number and an array and inserts the num so as to maintain order', function(){
    var number = 7, array = [1, 4, 5, 8, 9, 11];

    insertAtRightPlace(number, array);

    expect(array).toEqual([1, 4, 5, 7, 8, 9, 11]);
  });
});