Question

What is the best way to find if an object is in an array?

This is the best way I know:

function include(arr, obj) {   for (var i = 0; i < arr.length; i++) {     if (arr[i] == obj) return true;   } }  console.log(include([1, 2, 3, 4], 3)); // true console.log(include([1, 2, 3, 4], 6)); // undefined

Answer 1

As of ECMAScript 2016 you can use includes()

arr.includes(obj); 

If you want to support IE or other older browsers:

function include(arr,obj) {     return (arr.indexOf(obj) != -1); } 

EDIT: This will not work on IE6, 7 or 8 though. The best workaround is to define it yourself if it’s not present:

1. Mozilla’s (ECMA-262) version:

      if (!Array.prototype.indexOf)    {          Array.prototype.indexOf = function(searchElement /*, fromIndex */)       {        "use strict";       if (this === void 0 || this === null)        throw new TypeError();       var t = Object(this);      var len = t.length >>> 0;      if (len === 0)        return -1;       var n = 0;      if (arguments.length > 0)      {        n = Number(arguments[1]);        if (n !== n)          n = 0;        else if (n !== 0 && n !== (1 / 0) && n !== -(1 / 0))          n = (n > 0 || -1) * Math.floor(Math.abs(n));      }       if (n >= len)        return -1;       var k = n >= 0            ? n            : Math.max(len - Math.abs(n), 0);       for (; k < len; k++)      {        if (k in t && t[k] === searchElement)          return k;      }      return -1;    };   } 

2. Daniel James‘s version:

    if (!Array.prototype.indexOf) {    Array.prototype.indexOf = function (obj, fromIndex) {      if (fromIndex == null) {          fromIndex = 0;      } else if (fromIndex < 0) {          fromIndex = Math.max(0, this.length + fromIndex);      }      for (var i = fromIndex, j = this.length; i < j; i++) {          if (this[i] === obj)              return i;      }      return -1;    };  } 

3. roosteronacid‘s version:

    Array.prototype.hasObject = (    !Array.indexOf ? function (o)    {      var l = this.length + 1;      while (l -= 1)      {          if (this[l - 1] === o)          {              return true;          }      }      return false;    } : function (o)    {      return (this.indexOf(o) !== -1);    }  );