myUnshift.html

<script src="..\my-jsArrayMethods\simpletest.js"></script>
<script>
  // The unshift() method adds one or more elements to the beginning of an array.
  // It returns the new length of the array.

  // The unshift method inserts the given values to the beginning of an array-like object.
  // unshift is intentionally generic; 
    // this method can be called or applied to objects resembling arrays. 
      // unshift may not work on an object that does not contain a length property that is a number.
  
  // Parameters:
    // elementN: The elements to add to the front of the array.
  
  // Return Value:
    // the new length of the appended array.

  // Notes: 
    // this version of unshift will overwrite the native prototype Array.prototype.unshift.
  
  Array.prototype.unshift = function(elements) {

    var newLength = this.length + arguments.length;
    var updatedObj = this;
    var temp;

    if (Array.isArray(this)) {
      temp = [];
    } else {
      // handle an array-like object.
      temp = {};
      if (typeof this === 'object') {
        if (!this.length) {
          this.length = 0;
        }
      }
    }
    
    // store data from 'this' on temp variable.
    for (var i = 0; i < this.length; i++) {
      temp[i] = this[i];
    }
    
    // append the arguments to the called upon array or array-like object.
    for (var i = 0; i < newLength; i++) {
      if (i < arguments.length) {
        this[i] = arguments[i];
      } else {
         this[i]  = temp[i - arguments.length];
      }
      if (!Array.isArray(this)) {
        this.length ++;
      }
    }
    return this.length;   
  }

  tests({
    '1. If passed no arguments, it should return the length of the array it is called upon.': function() {
      var myArray = [];
      var unshifted = myArray.unshift();
      eq(unshifted, 0);
    },
    '2. It should prepend all elements to the array it is called upon.': function() {
      var myArray = ['a thing'];
      var unshifted = myArray.unshift('prepended thing');
      eq(myArray[0], 'prepended thing');
      eq(myArray[1], 'a thing');
      eq(unshifted, 2);
    },
    '3. It should create a length property equal to zero if applied or called without any arguments to an array-like object without a length property.': function() {
      var myObj = {};
      Array.prototype.unshift.call(myObj);
      eq(myObj.length, 0);
    },
    '4. It should shift elements onto an array-like object.': function() {
      var myObj = {length: 0};
      Array.prototype.unshift.call(myObj, 'first item', 'second item');
      eq(myObj.length, 2);
      eq(myObj[0], 'first item');
      eq(myObj[1], 'second item');
    },
  })
</script>