how to check if a function exists

Question

how to check if a function exists?

accepted answer here but it doesn't work

function sb_save(){
alert('saving');
}

$('button').on('click', function(){
 if ($.fn.sb_save){sb_save();}
});

<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
<button>CLICK</button>

How could it not be there? You declared it already, right? If it's a case that it might not be there, you can just easily check if is truthy by if(sb_save) or just by checking if it's type equals "function" — Kavian Rabbani, Jul 26 '20 at 15:35
`$.fn` is jquery object property. The function shown has nothing to do with jQuery. What would make you think that conditional would ever be truthy? — charlietfl, Jul 26 '20 at 15:37
Why are checking if `$.fn.sb_save` exists and later calling `sb_save`? — adiga, Jul 26 '20 at 15:37

score 2 · Accepted Answer · answered Jul 26 '20 at 15:37

2

function sb_save(){
alert('saving');
}

$('button').on('click', function(){
 if (typeof sb_save==="function"){
sb_save();
 }
});

<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
<button>Click</button>

answered Jul 26 '20 at 15:37

Asutosh

2

This is mentioned in the question linked by OP *"but it doesn't work"* – adiga Jul 26 '20 at 15:39
this condition seems to be truthy anytime. – Kavian Rabbani Jul 26 '20 at 15:39

Maestro · Answer 2 · 2020-07-26T15:48:16.760

0

function sb_save(){
    alert('saving');
}

$('button').on('click', function(){
    if (typeof sb_save === 'function') {
        sb_save();
    }
});

<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
<button>CLICK</button>

edited Jul 26 '20 at 15:48

answered Jul 26 '20 at 15:39

Maestro

*As of jQuery 3.3, jQuery.isFunction() has been deprecated. In most cases, its use can be replaced by typeof x === "function"* – Anurag Srivastava Jul 26 '20 at 15:40
1

You don't really need the `undefined` check – Anurag Srivastava Jul 26 '20 at 15:45

score -1 · Answer 3 · answered Jul 26 '20 at 15:39

Given the code example you show, you are trying to check if jQuery has been extended using that function:

if ($.fn.sb_save)

The way you're trying to call the function

sb_save();

shows this is not what you intended.

Instead, to simply check if sb_save is an executable object (a.k.a. function), use the most upvoted answer from the question you linked:

if (typeof sb_save === 'function')

function sb_save() {
  alert('saving');
}

$('button').on('click', function() {
  if (typeof sb_save === 'function') {
    sb_save();
  }
});

<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
<button>CLICK</button>

3 Answers3