How to Polyfill Array.prototype.includes() for IE8

Question

I'm trying to polyfill the array method includes() to work with IE8, which I need to support for a project and I don't want to use indexOf().

I know there's a polyfill, so I went to:

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/includes#Polyfill

And included it at the top of my script.

IE8 has limited support for Object.defineProperty() so I polyfilled it as well: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/defineProperties#Polyfill

Lastly, I needed to polyfill Object.keys(): https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/keys#Polyfill

Put together, my polyfills are:

if (!Object.keys) {
  Object.keys = (function() {
    'use strict';
    var hasOwnProperty = Object.prototype.hasOwnProperty,
        hasDontEnumBug = !({ toString: null }).propertyIsEnumerable('toString'),
        dontEnums = [
          'toString',
          'toLocaleString',
          'valueOf',
          'hasOwnProperty',
          'isPrototypeOf',
          'propertyIsEnumerable',
          'constructor'
        ],
        dontEnumsLength = dontEnums.length;

    return function(obj) {
      if (typeof obj !== 'function' && (typeof obj !== 'object' || obj === null)) {
        throw new TypeError('Object.keys called on non-object');
      }

      var result = [], prop, i;

      for (prop in obj) {
        if (hasOwnProperty.call(obj, prop)) {
          result.push(prop);
        }
      }

      if (hasDontEnumBug) {
        for (i = 0; i < dontEnumsLength; i++) {
          if (hasOwnProperty.call(obj, dontEnums[i])) {
            result.push(dontEnums[i]);
          }
        }
      }
      return result;
    };
  }());
}

function defineProperties(obj, properties) {
  function convertToDescriptor(desc) {
    function hasProperty(obj, prop) {
      return Object.prototype.hasOwnProperty.call(obj, prop);
    }

    function isCallable(v) {
      // NB: modify as necessary if other values than functions are callable.
      return typeof v === 'function';
    }

    if (typeof desc !== 'object' || desc === null)
      throw new TypeError('bad desc');

    var d = {};

    if (hasProperty(desc, 'enumerable'))
      d.enumerable = !!desc.enumerable;
    if (hasProperty(desc, 'configurable'))
      d.configurable = !!desc.configurable;
    if (hasProperty(desc, 'value'))
      d.value = desc.value;
    if (hasProperty(desc, 'writable'))
      d.writable = !!desc.writable;
    if (hasProperty(desc, 'get')) {
      var g = desc.get;

      if (!isCallable(g) && typeof g !== 'undefined')
        throw new TypeError('bad get');
      d.get = g;
    }
    if (hasProperty(desc, 'set')) {
      var s = desc.set;
      if (!isCallable(s) && typeof s !== 'undefined')
        throw new TypeError('bad set');
      d.set = s;
    }

    if (('get' in d || 'set' in d) && ('value' in d || 'writable' in d))
      throw new TypeError('identity-confused descriptor');

    return d;
  }

  if (typeof obj !== 'object' || obj === null)
    throw new TypeError('bad obj');

  properties = Object(properties);

  var keys = Object.keys(properties);
  var descs = [];

  for (var i = 0; i < keys.length; i++)
    descs.push([keys[i], convertToDescriptor(properties[keys[i]])]);

  for (var i = 0; i < descs.length; i++)
    Object.defineProperty(obj, descs[i][0], descs[i][1]);

  return obj;
}

if (!Array.prototype.includes) {
alert('test');

  defineProperties(Array.prototype, 'includes', {
    value: function(searchElement, fromIndex) {
                'use strict';

      if (this === null) {
        throw new TypeError('"this" is null or not defined');
      }

      // 1. Let O be ? ToObject(this value).
      var o = Object(this);

      // 2. Let len be ? ToLength(? Get(O, "length")).
      var len = o.length >>> 0;

      // 3. If len is 0, return false.
      if (len === 0) {
        return false;
      }

      // 4. Let n be ? ToInteger(fromIndex).
      //    (If fromIndex is undefined, this step produces the value 0.)
      var n = fromIndex | 0;

      // 5. If n ≥ 0, then
      //  a. Let k be n.
      // 6. Else n < 0,
      //  a. Let k be len + n.
      //  b. If k < 0, let k be 0.
      var k = Math.max(n >= 0 ? n : len - Math.abs(n), 0);

      function sameValueZero(x, y) {
        return x === y || (typeof x === 'number' && typeof y === 'number' && isNaN(x) && isNaN(y));
      }

      // 7. Repeat, while k < len
      while (k < len) {
        // a. Let elementK be the result of ? Get(O, ! ToString(k)).
        // b. If SameValueZero(searchElement, elementK) is true, return true.
        if (sameValueZero(o[k], searchElement)) {
          return true;
        }
        // c. Increase k by 1. 
        k++;
      }

      // 8. Return false
      return false;
    }
  });
}

To test the above script, I did:

var arr = ["one", "two", "three"];

alert( arr.includes('two') );

IE8 throws this error:

Object doesn't support this property or method.

I thought that by using polyfills, I would be able to add support for array includes() to IE8. What am I doing wrong? Any corrections or links to other polyfills are welcomed. No jQuery or other libraries. I just want to add support for includes() to IE.

Answer 1

You can simply use Array#indexOf to polyfill Array#includes.

For IE8, you will also need to polyfill Array#indexOf as it was only implemented in IE9.

if(!Array.prototype.includes){
   //or use Object.defineProperty
   Array.prototype.includes = function(search){
    return !!~this.indexOf(search);
  }
}
if(!Array.prototype.indexOf){
Array.prototype.indexOf = (function(Object, max, min){
  "use strict";
  return function indexOf(member, fromIndex) {
    if(this===null||this===undefined)throw TypeError("Array.prototype.indexOf called on null or undefined");

    var that = Object(this), Len = that.length >>> 0, i = min(fromIndex | 0, Len);
    if (i < 0) i = max(0, Len+i); else if (i >= Len) return -1;

    if(member===void 0){ for(; i !== Len; ++i) if(that[i]===void 0 && i in that) return i; // undefined
    }else if(member !== member){   for(; i !== Len; ++i) if(that[i] !== that[i]) return i; // NaN
    }else                           for(; i !== Len; ++i) if(that[i] === member) return i; // all else

    return -1; // if the value was not found, then return -1
  };
})(Object, Math.max, Math.min);
}

Array.prototype.includes = null;
Array.prototype.indexOf = null;
if(!Array.prototype.includes){
   console.log('Polyfilled Array.prototype.includes');
   //or use Object.defineProperty
   Array.prototype.includes = function(search){
    return !!~this.indexOf(search);
  }
}
if(!Array.prototype.indexOf){
 console.log("Polyfilled Array.prototype.indexOf");
Array.prototype.indexOf = (function(Object, max, min){
  "use strict";
  return function indexOf(member, fromIndex) {
    if(this===null||this===undefined)throw TypeError("Array.prototype.indexOf called on null or undefined");

    var that = Object(this), Len = that.length >>> 0, i = min(fromIndex | 0, Len);
    if (i < 0) i = max(0, Len+i); else if (i >= Len) return -1;

    if(member===void 0){ for(; i !== Len; ++i) if(that[i]===void 0 && i in that) return i; // undefined
    }else if(member !== member){   for(; i !== Len; ++i) if(that[i] !== that[i]) return i; // NaN
    }else                           for(; i !== Len; ++i) if(that[i] === member) return i; // all else

    return -1; // if the value was not found, then return -1
  };
})(Object, Math.max, Math.min);
}
var obj = {x: 1, y: 2};
var arr = [1, 'what', obj];
console.log('Array includes 1:',arr.includes(1));
console.log('Array includes \'what\':', arr.includes('what'));
console.log('Array includes obj:', arr.includes(obj));
console.log('Array includes 3:', arr.includes(3));