How to check if function exist?

Question

How to check if is function on jquery, but function is in another .js file?

validation.js:

if ($.isFunction('payment')) {
    $('[data-numeric]').payment('restrictNumeric');
    $('.cc-number').payment('formatCardNumber');
    $('.cc-exp').payment('formatCardExpiry');
    $('.cc-cvc').payment('formatCardCVC');
}

this is false because func payments is in the payments.js .

possible duplicate of [Javascript check if function exists](http://stackoverflow.com/questions/1042138/javascript-check-if-function-exists) — Liam, May 13 '15 at 13:15
You want to check if jQuery `$` has the function defined. Ex. `$.myFunc` — Tushar, May 13 '15 at 13:22
possible duplicate of http://stackoverflow.com/questions/5999998/how-can-i-check-if-a-javascript-variable-is-function-type — ambodi, May 13 '15 at 13:25
If it's specifically jQuery functions (though the fact that they are registered in jquery is pretty much irrelevant, a function is just a function regardless of where it is registered) there is also this [How to check jQuery plugin and functions exists?](http://stackoverflow.com/questions/5339876/how-to-check-jquery-plugin-and-functions-exists) — Liam, May 13 '15 at 13:26

score 36 · Answer 1 · answered May 13 '15 at 13:15

36

Try like this

if (typeof payment === "function")
{
  // Do something
}

answered May 13 '15 at 13:15

Anik Islam Abhi

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`if is function on jquery, but function is in another .js file` – Tushar May 13 '15 at 13:18

score 21 · Accepted Answer · answered May 13 '15 at 13:33

21

problem is solved. its works:

if ($.fn.payment) {
    //do something
}

answered May 13 '15 at 13:33

Haroldas

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3
9
36

score 9 · Answer 3 · answered May 13 '15 at 13:15

9

Try to check like as follows,

 if (typeof payment !== 'undefined' && $.isFunction(payment)) {
    $('[data-numeric]').payment('restrictNumeric');
    $('.cc-number').payment('formatCardNumber');
    $('.cc-exp').payment('formatCardExpiry');
    $('.cc-cvc').payment('formatCardCVC');
 }

answered May 13 '15 at 13:15

Shijin TR

7,516
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`if is function on jquery, but function is in another .js file` – Tushar May 13 '15 at 13:18
1

files are irrelevant in js @Tushar. The "exists" is whether it is in the current scope of the window. The "files" simply add objects(functions) to the scope. What are you getting at? – Liam May 13 '15 at 13:19
@Liam He want to check if jQuery `$` has the function defined. Ex. $.myFunc – Tushar May 13 '15 at 13:21

score 4 · Answer 4 · answered May 13 '15 at 13:16

You can check if a function exists using window

For example

var fn = window['NameOfTheFunction']; 
if(typeof fn === 'function') {
    doSomething();
}

If your function in payment.js is part of a self contained function, you need to set it to so the window object can "see" it by adding this in your self contained function:

window.NameOfTheFunction = NameOfTheFunction;

How to check if function exist?

4 Answers4

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