What does new function(settings){...}(jQuery.query || {}); mean in javascript?

Question

The code sample is here.

The big code chunk starts with

new function(settings) {

and ends with

}(jQuery.query || {}); // Pass in jQuery.query as settings object

What does this trick do?

Why does Eclipse find 2 errors here? Eclipse dislikes new at the beginning. May I just remove it? Also Eclipse wishes ] at the end to "to complete NewExpression".

What does this mean? How to write this with []?

possible duplicate of new function() with lower case "f" in JavaScript — Rob W
– Rob W, Commented Dec 19, 2011 at 12:07

MLN · Accepted Answer · 2011-12-19 12:07:31Z

4

This creates an anonymous function and invokes it with

(jQuery.query || {})

as the parameter.

try

new function(x){alert(x);}("foo");

in firebug.

answered Dec 19, 2011 at 12:07

MLN

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2 Comments

Dims Over a year ago

But what is jQuery.query? Should this be defined somewhere else?

Dims Over a year ago

I mean jQuery.query is also used in the body. Does it mean something?

Anders Tornblad · Accepted Answer · 2011-12-19 13:12:51Z

3

It is one way of creating a self-invoking javascript function. It's simply a function that is declared and invoked in one swift flick of the wrist.

http://sparecycles.wordpress.com/2008/06/29/advanced-javascript/

What Eclipse is complaining about is not really clear. The syntax is completely valid - it might just be that Eclipse cannot handle it properly.

EDIT: The argument that is passed: (jQuery.query || {}) passes jQuery.query to the function. If jQuery.query is null, false, zero or undefineded (falsey), an empty object literal will be passed instead, avoiding a null reference.

edited Dec 19, 2011 at 13:12

answered Dec 19, 2011 at 12:06

Anders Tornblad

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4 Comments

Dims Over a year ago

Isn't it possible to invoke code by just writing it inline in Javascript?

Dims Over a year ago

I mean if I can write new function(x){alert(x);}("foo"); then can't I just write alert("foo");?

nnnnnn Over a year ago

@Dims - putting code in an immediately executed function has the advantage that any working variables you create will have local scope in that function (and thus disappear when the function completes) rather than being added to the global scope, so you can keep a block of code self-contained. You wouldn't do it for just an alert since an alert isn't going to have any side effects. (There are some more obscure advantages in some situations, but I won't try to explain them here.)

Anders Tornblad Over a year ago

Mark as answer then, perhaps? :)

Sergio Tulentsev · Accepted Answer · 2011-12-19 12:19:58Z

1

The new function construction is defining a new function. It works in major browsers, but it is preferred to use slightly different syntax.

(function() {
    ...
})();

Here we define a function and then immediately call it. In your code, the function is also passed a parameter.

The Eclipse complaining is probably a bug.

edited Dec 19, 2011 at 12:19

answered Dec 19, 2011 at 12:09

Sergio Tulentsev

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