jQuery test for whether an object has a method?

Question

Is it possible to test whether a jQuery object has a particular method? I've been looking, but so far without success. Thanks!

Do you mean `!!$obj.method`? Or is this more complicated than that? — sdleihssirhc, Feb 24 '11 at 18:27
@Nyuszika7H My point was just check for truthiness. But it's hard to get that across with just `$obj.method`, so I added the bangs for clarification. — sdleihssirhc, Feb 24 '11 at 19:06
@sdleihssirhc No problem, there's [not much speed difference](http://jsperf.com/double-bang-in-if). — alexia, Feb 24 '11 at 19:08
You have a nice answer [here](http://stackoverflow.com/a/5159690/1257607) — DanielV, Jul 15 '15 at 12:12

score 46 · Accepted Answer · edited Feb 24 '11 at 19:45

46

This should work:

if (!!$.prototype.functionName)

edited Feb 24 '11 at 19:45

user113716

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answered Feb 24 '11 at 18:27

hunter

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score 23 · Answer 2 · answered Feb 24 '11 at 18:32

23

Because jQuery methods are prototype into a jQuery object, you can test it from the prototype object.

if( $.isFunction( $.fn.someMethod ) ) {
    // it exists
}

This uses the jQuery.isFunction()^[docs] method to see if $.fn.someMethod is indeed a function. (In jQuery jQuery.fn is a reference to the prototype object.)

answered Feb 24 '11 at 18:32

user113716

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+1. This is the only one that actually checks if it's a calalble function, and not just a member variable... – ircmaxell Feb 24 '11 at 19:11
2

For others who are perhaps as slow on the uptake as I am: if you are, for example, checking to see if the UI Tabs method exists, use `$.isFunction($.fn.tabs)`. Hey, I needed a concrete example; maybe someone else does, too. – Ryan Burney Jan 17 '13 at 17:17
Deprecated in 3.3.0 – JPollock May 21 '18 at 15:30

qwertymk · Answer 3 · 2011-02-25T06:19:39.143

5

try

if ($.fn.method) {
    $('a').method(...);
}

or

if ($.method) {
    $.method(...);
}

edited Feb 25 '11 at 06:19

answered Feb 24 '11 at 18:27

qwertymk

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-1, you're calling jQuery unneccessarily in the first example, that's more than 90% slower! http://jsperf.com/jquery-vs-jquery-fn – alexia Feb 24 '11 at 19:00
`if ($.method) {` doesn't work for me. I had to use `if ($.fn.method) {` – Kevin Wheeler Mar 21 '16 at 20:42

score 0 · Answer 4 · answered Apr 23 '15 at 13:13

//Simple function that will tell if the function is defined or not
function is_function(func) {
    return typeof window[func] !== 'undefined' && $.isFunction(window[func]);
}

//usage

if (is_function("myFunction") {
        alert("myFunction defined");
    } else {
        alert("myFunction not defined");
    }

score 0 · Answer 5 · answered Dec 07 '19 at 05:22

0

this worked for me

if (typeof myfunctionname === 'function')

answered Dec 07 '19 at 05:22

Jay Jara

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score -1 · Answer 6 · answered Feb 24 '11 at 18:29

-1

You should be able to look for undefined

if( typeof jQuery("*").foo === "undefined" ){
  alert("I am not here!");
}

answered Feb 24 '11 at 18:29

epascarello

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you could optimize a little by not getting every single element when they're not needed :) – Anurag Feb 24 '11 at 18:30

jQuery test for whether an object has a method?

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