JavaScript/jQuery equivalent of LINQ Any()

Question

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.

Posehn

Answer 1

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

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

Misdoubt

quick summary: some() executes the callback function once for each element present in the array until it finds one where callback returns a true value. If such an element is found, some() immediately returns true. Otherwise, some() returns false. – Bunkum

This is the right answer if you can use it. It is an equivalent function to Linq.Any() – Oringas

If you need IE8 compatibility, then this is not an option. – Brittni

Update: In ES6 / ECMAScript 2015, you can do myArray.some(c=>c) to mimic exactly what LINQ does with .Any(). Noting that in LINQ the .Any() method doesn't require a delegate, whereas .some() does. Attempting to call .some() without a delegate will result in an error as the delegate will be undefined. – Gaw

Answer 2

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

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

Rinker

I think you should avoid using this inside the is function when used for an array. Because you won't get the original type (so comparission using "===" will fail). I'd use array[i] instead. See this: jsfiddle.net/BYjcu/3 – Epidermis

This is interesting (my fiddle to confirm) but my gut reaction is to avoid this approach since it is operating a selection function $.fn.is over a collection that is not a jQuery selection (a native array). If there was a utility function like $.is I'd feel safer, but this appears to be an undocumented "feature" – Tbilisi

AFAIK jQuery selections are native arrays (or at least they use Array.prototype), and there is probably enough code in the wild relying on it that it can never change. This saying, this answer is almost six years old. These days you should be using native ES5 approach shown nearby, or something like LoDash/Underscore/etc. that has API specifically for dealing with native JS arrays. – Rinker

You're right, I did not notice the date on this answer. Sorry about that (and now I can't undo my downvote!) – Tbilisi

Answer 3

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.

Parashah

Was this supposed to be a comment or edit on their answer? It seems to only agree with that answer, adding a bit of context? – Walkway

Answer 4

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

Vasilikivasilis

*could (I think you meant to say) – Bunkum

@Simon_Weaver: No; he should not use for in to iterate arrays. – Vasilikivasilis

@SLaks, you have misunderstood Simon_Weaver's comment! "You could use an ordinary for loop." Rather than "You should..." – Cristoforo

Well it definitely says should right there in the text. You can’t say they were misunderstood when it is literally written there. – Walkway

Answer 5

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

Geof

Answer 6

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.

Sigmoid

actually, $.grep() is more like FindAll(Predicate<T>). – Newmown

@Groo: I didn't said that Any(Predicate<T>) is the most closest method to grep(), only is very near. I agree that FindAll(Predicate<T>) is much more close to it. But both are near. – Sigmoid

Answer 7

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);
}

Jeffryjeffy

I believe OP wanted to say with plain for (...) iterates over all of its members that use of for in can sometimes yield unexpected results (if Array.prototype is extended, or if you implicitly resize arrays). – Newmown

Answer 8

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');

Wearable