Calling javascript functions without parenthesis

Question

When i was reading some code of jquery then i found this in one of their widgets

    option: {
        _page: this._getPage,
        _panelInner: this._getPanelInner()
    },
    _getPage : function(){ //code goes here that returns something..},
    _getPanelInner : function(){ //code goes here that returns something..}

I wanna know how's the first this._getPage function is being called without parenthesis. And if functions can be called like this then why the next function _getPanelInner is being called with parenthesis..?

It's not called, a reference to the function is passed instead. var a = function() {}; var b = a; <--- here 2 variables refer to the same function. — zerkms
– zerkms, Commented Apr 2, 2015 at 8:34

Lix · Accepted Answer · 2015-04-02 08:43:50Z

3

_panelInner will hold the value returned by the _getPanelInner function while _page will hold a reference to the _getPage function. This means that the function would be able to be called in one of the following ways:

option._page()
this._getPage()

Both of these function calls would execute the same function but that function is not called automatically (according to the code that is displayed).

edited Apr 2, 2015 at 8:43

answered Apr 2, 2015 at 8:35

Lix

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4 Comments

zerkms Over a year ago

"return value of the _getPanelInner function" --- this does not sound right.

Lix Over a year ago

I mean the "return value" of the function, @zerkms. I'm not sure how else to phrase that...

zerkms Over a year ago

I agree it's not easy to phrase it concisely though :-)

Kapil Garg Over a year ago

@zerkms '_getPanelInner' is returning an object so i think '_panelInner' is holding that object

eladcon · Accepted Answer · 2015-04-02 08:34:18Z

3

It's not getting called, it's only having a reference to the function so later you can do:

option._page();

answered Apr 2, 2015 at 8:34

eladcon

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