How can I check whether a particular element is inside an array? I don't want to manually write a loop for this; instead I want to use a JavaScript built-in function, maybe something equivalent to

new Array(0,1,2,3,6,9,12,15,18).Contains(5)  //return false
new Array(0,1,2,3,6,9,12,15,18).Contains(1)   //return true

How can I check whether a particular element is inside an array? I don't want to manually write a loop for this; instead I want to use a JavaScript built-in function, maybe something equivalent to

new Array(0,1,2,3,6,9,12,15,18).Contains(5)  //return false
new Array(0,1,2,3,6,9,12,15,18).Contains(1)   //return true

• javascript
• arrays

6 Answers 6

The Array object does have an indexOf function, that will return -1 if the object does not exist. However, IE does not support this function.

Regardless, how do you think it is going to locate the item under the scenes? It will have to loop! Just because there's a built-in function does not mean that it is magical.

You could also write an extension method, as explained in this thread.

Array.prototype.contains = function(obj) {
  var i = this.length;
  while (i--) {
    if (this[i] === obj) {
      return true;
    }
  }
  return false;
}
And now you can simply use the following:

alert([1, 2, 3].contains(2)); // => true
alert([1, 2, 3].contains('2')); // => false

As @Josh Stodola said, the indexOf function is what you need, but this function was introduced on JavaScript 1.6, for patibility you can use this implementation from the Mozilla team, is exactly the one used in Firefox and SpiderMonkey:

if (!Array.prototype.indexOf)
{
  Array.prototype.indexOf = function(elt /*, from*/)
  {
    var len = this.length >>> 0;

    var from = Number(arguments[1]) || 0;
    from = (from < 0)
         ? Math.ceil(from)
         : Math.floor(from);
    if (from < 0)
      from += len;

    for (; from < len; from++)
    {
      if (from in this &&
          this[from] === elt)
        return from;
    }
    return -1;
  };
}

Source: MDC

Looks like a job for jQuery.inArray

inArray: function( elem, array ) {
    for ( var i = 0, length = array.length; i < length; i++ )
    // Use === because on IE, window == document
        if ( array[ i ] === elem )
            return i;

    return -1;
}

There is no such method in javascript.

Some library (e.g. jquery) have similar method, but they use loops internally.

Ah, there is a way not to loop and it is pretty simple, people just do not think outside the box.

Array.prototype.contains = function(){     
    var joined = this.join("-~-");
    var re = new RegExp("(^|-~-)" + arguments[0] + "($|-~-)");   
    return joined.match(re) !== null;
}

var arr = ["a","b","c","d"];   
alert(arr.contains("a"));
alert(arr.contains("b"));
alert(arr.contains("c"));
alert(arr.contains("d"));
alert(arr.contains("e"));

Loop mom, no loops!