How to add function to specific string in javascript

Question

I have a string in javascript

var Foo = "Bar";

I have a function that does a manipulation on this string. to add this function to the string I did this

String.prototype.func = function(){
   // code
}

But this function will work for every string. I want this function to be called only from my variable Foo

Quentin · Accepted Answer · 2014-08-15 13:16:41Z

6

So apply it only to the string in the variable Foo.

You'll need to make it a String object rather than a primitive though.

var foo = new String("Bar");
foo.func = function () { ... };

answered Aug 15, 2014 at 13:16

Quentin

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6 Comments

James Hay Over a year ago

It should probably just be var foo = "Bar"

James Hay Over a year ago

Ah I see. Carry on then.

Quentin Over a year ago

That's why I said "You'll need to make it a String object rather than a primitive though."

Felix Kling Over a year ago

But of course using a string object may introduce other problems.

Pointy Over a year ago

@Khalid not always - it will be called automatically in some cases. You really have no other choice than something like this.

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Ali Motevallian · Accepted Answer · 2014-08-15 13:25:45Z

0

If you want it to work only on your variable Foo then simply do the following:

var Foo = new String("Bar");
Foo.func = function(){
    //code
};

You don't need to add the function to the prototype of String.

edited Aug 15, 2014 at 13:25

answered Aug 15, 2014 at 13:18

Ali Motevallian

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2 Comments

Felix Kling Over a year ago

You wouldn't be able to call the function though. Primitives don't have properties. What happens behind the scene is that JS converts the primitive to an object, but discards the object again.

Khalid Over a year ago

I tried it before but didn't work. TypeError: undefined is not a function

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