Best way to find if an item is in a JavaScript array?

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        if (arr[i] == obj) return true;
    }
}


include([1,2,3,4], 3); // true
include([1,2,3,4], 6); // undefined

Answer

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);
     }
   );