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JavaScript Array Contains

Javascript objects are really nice, but sometimes they are missing some useful little functions/methods. The example above is with Arrays. It's really nice to know whether or not an item is contained within your array. Well you can write a function that takes the array and the item you're checking for, but it's much cleaner to add the contains( item ) method to the Array object.

Extending JavaScript Arrays

/**
 * Array.prototype.[method name] allows you to define/overwrite an objects method
 * needle is the item you are searching for
 * this is a special variable that refers to "this" instance of an Array.
 * returns true if needle is in the array, and false otherwise
 */
Array.prototype.contains = function ( needle ) {
   for (i in this) {
       if (this[i] == needle) return true;
   }
   return false;
}

Usage

// Now you can do things like:
var x = Array();
if (x.contains('foo')) {
   // do something special
}

Subscribe to The Thread

  1. V1

    I suggest making it more strict,

    if (this[i] == needle) return true;

    to:

    if (this[i] === needle) return true;

    for example, 1 is the same as true. Unless you do ===

    Reply ↓
  2. Alex

    Thank you V1, you’re absolutely right. That should definitely be a ===.

    Reply ↓
  3. James

    “i” should be declared locally (by using a var statement). Currently you’re setting it as a global variable. Also, you shouldn’t be using the “for(i in something)” construct for arrays. Instead use a traditional for or while loop; they’re much quicker.

    Reply ↓
  4. Jhuni

    Here is how I would write it, coming in at a mere 83 kb minified:

    var contains = function( arr, value ) {

	var i = 0, len = arr.length;

	while( i < len && arr[i] != value ) {

		i++;

	}

	return i != len;

};
    Reply ↓
  5. einstein

    Thank you, It really worked.

    Reply ↓
  6. David Chambers

    Nicer still would be to write it like this:

    function contains(arr, value) {
    var i = arr.length;
    while (i--) {
        if (arr[i] === value) return true;
    }
    return false;
}
    Reply ↓
  7. John Doe

    /**
    * is_array
    *
    * @param mixed input
    * @return bol
    */

    function is_array(obj) {
    if (obj.constructor.toString().indexOf(‘Array’) == -1) {
    return false;
    }
    return true;
    }

    /**
    * contains
    *
    * @param mixed input
    * @param string value
    * @return bol
    */

    function contains(input, value) {
    if (!is_array(input)) {
    if (input.indexOf(value) != -1) {
    return true;
    }
    }
    else {
    var i = input.length;
    while (i–) {
    if (input[i] === value) {
    return true;
    }
    }
    }
    return false;
    }

    Reply ↓

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