es2016.js

//----------------------------------------------------------------------
//
// ECMAScript 2016 Polyfills
//
//----------------------------------------------------------------------

(function (global) {
  "use strict";
  var undefined = (void 0); // Paranoia

  // Helpers

  function isSymbol(s) {
    return (typeof s === 'symbol') || ('Symbol' in global && s instanceof global.Symbol);
  }

  function define(o, p, v, override) {
    if (p in o && !override)
      return;

    if (typeof v === 'function') {
      // Sanity check that functions are appropriately named (where possible)
      console.assert(isSymbol(p) || !('name' in v) || v.name === p || v.name === p + '_', 'Expected function name "' + p.toString() + '", was "' + v.name + '"');
      Object.defineProperty(o, p, {
        value: v,
        configurable: true,
        enumerable: false,
        writable: true
      });
    } else {
      Object.defineProperty(o, p, {
        value: v,
        configurable: false,
        enumerable: false,
        writable: false
      });
    }
  }


  // Snapshot intrinsic functions
  var $isNaN = global.isNaN;

  var abs = Math.abs,
      floor = Math.floor,
      max = Math.max,
      min = Math.min;

  //----------------------------------------
  // 7 Abstract Operations
  //----------------------------------------

  // 7.1.4
  function ToInteger(n) {
    n = Number(n);
    if ($isNaN(n)) return 0;
    if (n === 0 || n === Infinity || n === -Infinity) return n;
    return ((n < 0) ? -1 : 1) * floor(abs(n));
  }

  // 7.1.13 ToObject
  function ToObject(v) {
    if (v === null || v === undefined) throw TypeError();
    return Object(v);
  }

  // 7.1.15 ToLength ( argument )
  function ToLength(v) {
    var len = ToInteger(v);
    if (len <= 0) {
      return 0;
    }
    return min(len, 0x20000000000000 - 1); // 2^53-1
  }

  //----------------------------------------
  // 7.2 Testing and Comparison Operations
  //----------------------------------------

  // 7.2.10 SameValueZero(x, y)
  function SameValueZero(x, y) {
    if (typeof x !== typeof y) return false;
    switch (typeof x) {
    case 'undefined':
      return true;
    case 'number':
      if (x !== x && y !== y) return true;
      return x === y;
    case 'boolean':
    case 'string':
    case 'object':
    default:
      return x === y;
    }
  }

  //----------------------------------------------------------------------
  //
  // ECMAScript 2016
  //
  //----------------------------------------------------------------------

  // https://github.com/tc39/Array.prototype.includes/
  define(
    Array.prototype, 'includes',
    function includes(target) {
      var fromIndex = arguments[1];

      var o = ToObject(this);
      var len = ToLength(o["length"]);
      if (len === 0) return false;
      var n = ToInteger(fromIndex);
      if (n >= 0) {
        var k = n;
      } else {
        k = len + n;
        if (k < 0) k = 0;
      }
      while (k < len) {
        var elementK = o[k];
        if (SameValueZero(o[k], target))
          return true;
        k += 1;
      }
      return false;
    });

}(this));