How to override function with variable number of parameters in javascript?

Question

I want to override jQuery's hide() function on my object. I want it to call my onHide() function and then call original hide().

How to accomplish this?

The simplest code won't pass parameters I guess:

myobject.oldhide = myobject.hide;
myobject.onHide = function() {
   // something
};
myobject.hide = function() {
   this.onHide();
   this.oldhide();
}

jQuery's hide() accepts up to 3 parameters. Can I just define 3 of them?

myobject.oldhide = myobject.hide;
myobject.onHide = function() {
   // something
};
myobject.hide = function(a,b,c) {
   this.onHide();
   this.oldhide(a,b,c);
}

Alnitak · Accepted Answer · 2012-02-01 17:43:55Z

6

You can use .apply() to call the original:

this.oldhide.apply(this, arguments);

which will call oldhide with whatever argument list was passed to your own function, which need not have any declared parameters:

myobject.oldhide = myobject.hide;

myobject.onHide = function() {
   // something
};

myobject.hide = function() {
   this.onHide();
   this.oldhide.apply(this, arguments);
}

answered Feb 1, 2012 at 17:43

Alnitak

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4 Comments

Dims Over a year ago

Doesn't this.oldhide.apply(this, arguments) will do the same as this.oldhide(arguments)?

Matthew Flaschen Over a year ago

@Dims, no. With the second, arguments is passed as the first (duration) parameter of jQuery's hide.

Dims Over a year ago

Ah, got it, thanks! And on general question, there is no other way to call old version of function other than keeping it in temporary variable?

Alnitak Over a year ago

@Dims no, the temporary variable is pretty much the only way.

Matthew Flaschen · Accepted Answer · 2012-02-01 17:43:45Z

2

Yes, the ones that are not passed in will just be undefined.

answered Feb 1, 2012 at 17:43

Matthew Flaschen

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4 Comments

Alnitak Over a year ago

but the code will require changes if a new version of .hide() that takes four parameters comes along....

Matthew Flaschen Over a year ago

@Alnitak, only the function definition will change. The callers of the function don't have to change anything.

Alnitak Over a year ago

sure, but that's why arguments exists - you don't need to declare parameters a, b, c solely to pass them on verbatim to another function.

Matthew Flaschen Over a year ago

@Alnitak, agreed. The main reason would be if they were also used by the wrapper.

sinemetu1 · Accepted Answer · 2012-02-01 21:10:33Z

0

You could cache the old hide using $.proxy.

    myobject.oldhide = $.proxy(myobject.hide, myobject);
    myobject.onHide = function() {
       // something
    };
    //a, b, and c parameters don't have to be passed
    //but if they are they will be forwarded to the old hide.
    //Using $.proxy will preserve the way the old function takes parameters.
    myobject.hide = function(a, b, c) {
       this.onHide();
       this.oldhide(a, b, c);
    };

edited Feb 1, 2012 at 21:10

answered Feb 1, 2012 at 18:03

sinemetu1

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2 Comments

Dims Over a year ago

I don't understand, how parameters for hide() will pass to oldhide()? For example, if I write myobject.hide(12); from my point of view 12 will be lost since this.oldhide() does not pass it further. Is it true?

sinemetu1 Over a year ago

@Dims I have edited to include information about parameter passing.

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