JavaScript/jQuery equivalent of LINQ Any()

Is there an equivalent of IEnumerable.Any(Predicate<T>) in JavaScript or jQuery?

I am validating a list of items, and want to break early if error is detected. I could do it using $.each, but I need to use an external flag to see if the item was actually found:

var found = false;
$.each(array, function(i) {
    if (notValid(array[i])) {
        found = true;
    }
    return !found;
});

What would be a better way? I don't like using plain for with JavaScript arrays because it iterates over all of its members, not just values.

These days you could actually use Array.prototype.some (specced in ES5) to get the same effect:

array.some(function(item) {
    return notValid(item);
});

You could use variant of jQuery is function which accepts a predicate:

$(array).is(function(index) {
    return notValid(this);
});

Xion's answer is correct. To expand upon his answer:

jQuery's .is(function) has the same behavior as .NET's IEnumerable.Any(Predicate<T>).

From http://docs.jquery.com/is:

> Checks the current selection against an expression and returns true, if at least one element of the selection fits the given expression.

You should use an ordinary for loop (not for ... in), which will only loop through array elements.

You might use array.filter (IE 9+ see link below for more detail)

[].filter(function(){ return true|false ;}).length > 0;

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/filter

I suggest you to use the $.grep() method. It's very close to IEnumerable.Any(Predicate<T>):

$.grep(array, function(n, i) {
  return (n == 5);
});

Here a working sample to you: http://jsfiddle.net/ErickPetru/BYjcu/.

2021 Update

This answer was posted more than 10 years ago, so it's important to highlight that:

1. When it was published, it was a solution that made total sense, since there was nothing native to JavaScript to solve this problem with a single function call at that time;
2. The original question has the jQuery tag, so a jQuery-based answer is not only expected, it's a must. Down voting because of that doesn't makes sense at all.
3. JavaScript world evolved a lot since then, so if you aren't stuck with jQuery, please use a more updated solution! This one is here for historical purposes, and to be kept as reference for old needs that maybe someone still find useful when working with legacy code.

I would suggest that you try the JavaScript for in loop. However, be aware that the syntax is quite different than what you get with a .net IEnumerable. Here is a small illustrative code sample.

var names = ['Alice','Bob','Charlie','David'];
for (x in names)
{
    var name = names[x];
    alert('Hello, ' + name);
}

var cards = { HoleCard: 'Ace of Spades', VisibleCard='Five of Hearts' };
for (x in cards)
{
    var position = x;
    var card = card[x];
    alert('I have a card: ' + position + ': ' + card);
}

Necromancing.
If you cannot use array.some, you can create your own function in TypeScript:

interface selectorCallback_t<TSource> 
{
    (item: TSource): boolean;
}


function Any<TSource>(source: TSource[], predicate: selectorCallback_t<TSource> )
{
    if (source == null)
        throw new Error("ArgumentNullException: source");
    if (predicate == null)
        throw new Error("ArgumentNullException: predicate");

    for (let i = 0; i < source.length; ++i)
    {
        if (predicate(source[i]))
            return true;
    }

    return false;
} // End Function Any

Which transpiles down to

function Any(source, predicate) 
 {
    if (source == null)
        throw new Error("ArgumentNullException: source");
    if (predicate == null)
        throw new Error("ArgumentNullException: predicate");
    for (var i = 0; i < source.length; ++i) 
    {
        if (predicate(source[i]))
            return true;
    }
    return false;
}

Usage:

var names = ['Alice','Bob','Charlie','David'];
Any(names, x => x === 'Alice');