Javascript concatenate a function similar to how text can be added

Question

In javscript we can do this

var text = "the original text";

text+=";Add this on";

If a library has a function already defined (e.g)

//In the js library
library.somefunction = function() {...};

Is there a way to add something on so that I can have two functions run?

var myfunction = function() {...};

Something like:

library.somefunction += myfunction

So that both myfunction() and the original library.somefunction() are both run?

Do you want the library's function to be changed to run both the original function and your custom function or do you want a new function that runs both? — Qantas 94 Heavy
– Qantas 94 Heavy, Commented May 7, 2013 at 8:19

Peter Bartels · Accepted Answer · 2013-05-07 15:46:29Z

1

You can use this kind of code (leave scope empty to use default scope):

var createSequence = function(originalFn, newFn, scope) {
    if (!newFn) {
        return originalFn;
    }
    else {
        return function() {
            var result = originalFn.apply(scope || this, arguments);
            newFn.apply(scope || this, arguments);
            return result;
        };
    }
}

Then:

var sequence = createSequence(library.somefunction, myFunction);

edited May 7, 2013 at 15:46

answered May 7, 2013 at 8:20

Peter Bartels

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1 Comment

Peter Bartels Over a year ago

Hi rab, I checked it and it was not passing the scope at originalFn.apply. Fixed that now

Andrei Nemes · Accepted Answer · 2013-05-07 08:30:33Z

0

I think what you want to create is a Hook (function) - you want to call library.somefunction but add a bit of your own code to run before. If that's the case, you can make your myfunction either call or return the library function after it's done with your bit of code.

var myfunction = function() {

    // your code
    // ...

    return library.somefunction();
}

answered May 7, 2013 at 8:30

Andrei Nemes

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1 Comment

Tarang Over a year ago

I also need to ensure that myfunction() is hooked in when library.somefunction() is called

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