How can you check if a function in jQuery is empty?

Question

How would you check if the function that does exist and is defined, is empty or not? For example:

function foo(){
   // empty
}

function bar(){
   alert('something');
   // not empty
}

Is there a function or a a simple way to check this?

Are you specifically interested in a JQuery way to do it? (JQuery != JS) — nico
– nico, Commented Aug 2, 2012 at 16:41
@Nico, well no, JS would of course also be fine. I just thought there would maybe be a jQuery function in existence already that I was overlooking. — Joey
– Joey, Commented Aug 2, 2012 at 16:45
@Juhana, checking if user assigned callbacks in my jQuery plugin meet requirements. — Joey
– Joey, Commented Aug 2, 2012 at 16:45

adeneo · Accepted Answer · 2012-08-02 16:54:02Z

3

It's not really very useful, and generally not a good idea, but you could do:

function foo(){

}

function bar(){
   alert('something');
   // not empty
}

console.log('foo is empty :' + isEmpty(foo));
console.log('bar is empty :' + isEmpty(bar));

function isEmpty(f) {
  return typeof f === "function" && /^function [^(]*\(\)[ ]*{(.*)}$/.exec(
     f.toString().replace(/\n/g, "")
   )[1].trim() === "";
}

FIDDLE

If it's just to check a callback, the normal way would be just to check if the callback is a function:

if (typeof callback === 'function') callback.call();

EDIT:

To also disregard comments :

function isEmpty(f) {
  return typeof f === "function" && /^function [^(]*\(\)[ ]*{(.*)}$/.exec(
     f.toString().replace(/\n/g, "").replace(/(\/\*[\w\'\s\r\n\*]*\*\/)|(\/\/[\w\s\']*)|(\<![\-\-\s\w\>\/]*\>)/g, '')
   )[1].trim() === "";
}

FIDDLE

edited Aug 2, 2012 at 16:54

answered Aug 2, 2012 at 16:47

adeneo

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3 Comments

JJJ Over a year ago

Nice, but won't work if there are comments inside the function.

adeneo Over a year ago

No it won't, and then the function would'nt really be empty either!

Joey Over a year ago

Thanks for the lengthy answer! Guess there isn't a simple way to check and i'll just check if the callback is indeed a function.

Micah Henning · Accepted Answer · 2012-08-02 17:09:39Z

1

A function could be empty but still be passed variables. This would error in adeneo's function:

function bar(t) { }

Modifying the regex, here is the same function with support for variables:

function isEmpty(f) {
  return typeof f === "function" && /^function [^(]*\([^)]\)[ ]*{(.*)}$/.exec(
     f.toString().replace(/\n/g, "").replace(/(\/\*[\w\'\s\r\n\*]*\*\/)|(\/\/[\w\s\']*)|(\<![\-\-\s\w\>\/]*\>)/g, '')
   )[1].trim() === "";
}

answered Aug 2, 2012 at 17:09

Micah Henning

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