core-js/internals/array-includes.js

Standard library

var toIndexedObject = require('../internals/to-indexed-object');
var toLength = require('../internals/to-length');
var toAbsoluteIndex = require('../internals/to-absolute-index');

// `Array.prototype.{ indexOf, includes }` methods implementation
// false -> Array#indexOf
// https://tc39.github.io/ecma262/#sec-array.prototype.indexof
// true  -> Array#includes
// https://tc39.github.io/ecma262/#sec-array.prototype.includes
module.exports = function (IS_INCLUDES) {
  return function ($this, el, fromIndex) {
    var O = toIndexedObject($this);
    var length = toLength(O.length);
    var index = toAbsoluteIndex(fromIndex, length);
    var value;
    // Array#includes uses SameValueZero equality algorithm
    // eslint-disable-next-line no-self-compare
    if (IS_INCLUDES && el != el) while (length > index) {
      value = O[index++];
      // eslint-disable-next-line no-self-compare
      if (value != value) return true;
    // Array#indexOf ignores holes, Array#includes - not
    } else for (;length > index; index++) if (IS_INCLUDES || index in O) {
      if (O[index] === el) return IS_INCLUDES || index || 0;
    } return !IS_INCLUDES && -1;
  };
};