JQuery check if variable is function

Question

How do I check if the return variable is a function?

var testController = function() {
  alert('123');
}

$(function() {
  $('[mfour]').each(function(e, t) {
    var a = $(t).attr('mfour');
    console.log($.isFunction(testController));
    console.log($.isFunction(a));
  })
});

<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.11.1/jquery.min.js"></script>

<div mfour="testController">asd</div>

Notice that on first console.log returns TRUE when the function name is hard-coded while on the second console.log if the variable is being evaluated returns FALSE.

It is kind of weird because var a returns testController.

Here's the jsFiddle.

My goal here is to run certain functions base on the mfour attribute. So in the example above, testController will run testController function.

`attr()` will always return a string, never a function. The fact that it might be the *name* of a function is irrelevant. — Paul Roub, Sep 15 '15 at 14:14
I guess you would rather want something like http://stackoverflow.com/q/5848700/218196 . — Felix Kling, Sep 15 '15 at 14:19
You really should put all functions in an object and then just access it with `myObj[funcName]`. — Felix Kling, Sep 15 '15 at 14:21
Use `typeof yourVar === "function"` instead of `$.isFunction()`, it's faster. — starikovs, Sep 15 '15 at 14:35

mplungjan · Answer 1 · 2015-09-15T14:23:39.543

2

Try using window[varname] - assuming the function is in global scope

like this

DEMO

var testController = function() {
    alert('123');
}

$(function() {
    $('[mfour]').each(function(e, t) {
        var a = $(t).attr('mfour');
        console.log($.isFunction(testController));
        console.log($.isFunction(window[a]));
        console.log(typeof window[a] === "function");
    })
});

<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.11.1/jquery.min.js"></script>
<div mfour="testController">Hello</div>

edited Sep 15 '15 at 14:23

answered Sep 15 '15 at 14:19

mplungjan

155,085
27
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It doesn't work either [link] (http://jsfiddle.net/nqmwjsp2/2/) – basagabi Sep 15 '15 at 14:20
1

As I said: "assuming the function is in global scope" yours is in the onload – mplungjan Sep 15 '15 at 14:21
@user1781041: The function in your example is not global. – Felix Kling Sep 15 '15 at 14:21
Here is a fixed fiddle http://jsfiddle.net/mplungjan/uu8qrqfL/ – mplungjan Sep 15 '15 at 14:22
@user1781041 And as explained in other comments, all you have is a string, if it's in the global scope, you can access it, if it's private, you may not have access to it. – Juan Mendes Sep 15 '15 at 14:23
@mplungjan, your fiddle is working but mine is not (http://jsfiddle.net/nqmwjsp2/3/). I just copy-pasted yours to mine. Though I notice that yours is set to "No wrap - in " while mine is "onLoad". Any difference between the two? – basagabi Sep 15 '15 at 14:31
Yes THAT. The scope is global in mine in yours it is the jquery load scope – mplungjan Sep 15 '15 at 14:54

Juan Mendes · Accepted Answer · 2015-09-15T15:37:50.783

In your example, to get a reference to the testFunction if it is in scope, you can use eval. Yes, I said it, eval, so you have to know that the string could be manipulated by the user to run malicious code if you don't sanitize it for function names;

var testController = function() {
  alert('123');
}

$(function() {
  $('[mfour]').each(function(e, t) {
    var a = eval($(t).attr('mfour'));
    console.log($.isFunction(testController));
    console.log($.isFunction(a));
  })
});

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<div mfour="testController">Hello</div>

Swaprks · Answer 3 · 2015-09-15T14:34:11.540

1

To check if the variable is a function just add a check

typeof variableName

It will return the type of variable.

Dude..

If possible, add your function to an object. Like below

var obj = {
    testController: function(){
       alert('123');
    }
};

    $(function() {
        $('[mfour]').each(function(e, t) {
            var a = $(t).attr('mfour');
            console.log($.isFunction(obj[a]));
        })
    });

edited Sep 15 '15 at 14:34

answered Sep 15 '15 at 14:23

Swaprks

1,503
11
15

1

Maybe `$.isFunction(obj[a])`? – starikovs Sep 15 '15 at 14:33

JQuery check if variable is function

3 Answers3