JavaScript equivalent of PHP's in_array()

Question

Is there a way in JavaScript to compare values from one array and see if it is in another array?

Similar to PHP's in_array function?

Answer 1

If you only want to check if a single value is in an array, then Paolo's code will do the job. If you want to check which values are common to both arrays, then you'll want something like this (using Paolo's inArray function):

function arrayIntersect(a, b) {
    var intersection = [];

    for(var i = 0; i < a.length; i++) {
        if(inArray(b, a[i]))
            intersection.push(a[i]);
    }

    return intersection;
}

This wil return an array of values that are in both a and b. (Mathematically, this is an intersection of the two arrays.)

EDIT: See Paolo's Edited Code for the solution to your problem. :)

Answer 2

An equivalent of in_array with underscore is _.indexOf

Examples:

_.indexOf([3, 5, 8], 8); // returns 2, the index of 8 _.indexOf([3, 5, 8], 10); // returns -1, not found

Answer 3

Array.indexOf was introduced in JavaScript 1.6, but it is not supported in older browsers. Thankfully the chaps over at Mozilla have done all the hard work for you, and provided you with this for compatibility:

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;
  };
}

There are even some handy usage snippets for your scripting pleasure.

Answer 4

jQuery solution is available, check the ducumentation here: http://api.jquery.com/jquery.inarray/

$.inArray( 10, [ 8, 9, 10, 11 ] );

Answer 5

If you are going to use it in a class, and if you prefer it to be functional (and work in all browsers):

inArray: function(needle, haystack)
{
    var result = false;

    for (var i in haystack) {
        if (haystack[i] === needle) {
            result = true;
            break;
        }
    }

    return result;
}

Hope it helps someone :-)