Check if javascript function exist with variable and execute it

Question

I have a popup system in my project. With a name, for example 'addnews', it knows which popup content to add and which script is necessary to handle the form. Up until now after completion I always did the same thing. Now, in some cases, I want to do something different.

Now I want to add a JavaScript function with that same name, like previous example 'addnews()', and check if that function exist. If it does run it, else do the standard things. (1)

Also executing a function with that name as variable doesn't seem to work. (2)

var functionName = 'addnews';

if (typeof functionName == 'function') { // (1) typeof functionName = string
    window[functionName](); // (2) this doesn't work for me
} else {
    // Do something standard
}

function addnews() {
    // Do something special
}

I'm not quite sure what you are trying to achieve. Why do you have to test whether a function exists? What is the overal problem you are trying to solve? "Up until now after completion I always did the same thing. Now, in some cases, I want to do something different." I guess that's your core problem, but in order to help you properly, you have to elaborate on this. — Felix Kling
– Felix Kling, Commented Feb 10, 2013 at 0:13

Mic · Accepted Answer · 2013-02-10 00:27:18Z

3

If you use this code in a document and it is not loaded complitelly your code will not find the function addnews() because it is not declare before this code.

Like in the comments: you need to use

if (typeof window[functionName] == 'function')

edited Feb 10, 2013 at 0:27

answered Feb 10, 2013 at 0:18

Mic

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3 Comments

Mic Over a year ago

do you know his complete code? :) i use this code in some projects too and it works fine.

Marvin Rabe Over a year ago

typeof functionName is always a string.

Mic Over a year ago

yes your are right. but eval = evil :) your should use if (typeof window[functionName] == 'function')

Marvin Rabe · Accepted Answer · 2013-02-10 00:31:29Z

0

This will do it:

if (typeof eval(functionName) == 'function') { 
    eval(functionName+'()');
} else {
    // Do something standard
}

Update: Only use this if the answer of Mic doesnt work (whyever). Like he said eval is pretty dangerous.

edited Feb 10, 2013 at 0:31

answered Feb 10, 2013 at 0:17

Marvin Rabe

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1 Comment

Felix Kling Over a year ago

eval is only dangerous when the input can potentially come from a different source than the user or the website itself (e.g. input from other users). Apart from potentially being dangerous, using it just leads to harder to maintain code and (possibly unnecessary) performance overhead.

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