strange anonymous javascript function call

Question

I was looking at this very cool snippet and i came across this weird line in the js and deleting that prevent the function from being invoked

!+-+-+!+-+-+!+-+-+!+-+-+!+-+-+!+-+-+!+-+-+!+-+-+!
function(d, w){
   ...
}(document, window);

,i wrapped the function with ( ) as it supposed to be and it works as intended.

(function(d, w){
    ...
})(document, window);

so my question is what is that weird line and why does it work? my wild guest is that it is some kind IIFE...

To elaborate on the the duplicate: the `+`, `-`, and `!` are all unary operators doing the same thing as the lone `!` in the linked duplicate. — apsillers, Apr 23 '13 at 13:21
@MimiEAM Correct, only one `+`, `-`, or `!` is needed for the function to be parsed as a function expression (rather than a function declaration). — apsillers, Apr 23 '13 at 15:39

tessi · Accepted Answer · 2013-05-01T13:55:44.050

And you are right, it is an Immediately-Invoked Function Expression (IIFE)

You can rewrite

!+-+-+!+-+-+!+-+-+!+-+-+!+-+-+!+-+-+!+-+-+!+-+-+!
function(d, w){
   ...
}(document, window);

to

!function() {
    ...
}()

and it still works. This is because ! is a unary operator (just like +, -, and ~ -- see https://developer.mozilla.org/en-US/docs/JavaScript/Guide/Expressions_and_Operators). After an unary operator an expression is expected (and evaluated!). The expression can be a function call.

However

!function() {
    ...
}()

is just another expression, so you can put another unary operator in front of it:

+!function() {
    ...
}()

You can continue this pattern as you wish.

Note: Invoking an anonymous function this way, ignores the return value of the function. So only use this, if you are not interested in the return value.

Edit: Added an excellent reference to http://benalman.com/news/2010/11/immediately-invoked-function-expression/ which Daff mentioned in his answer.

score 4 · Answer 2 · answered Apr 23 '13 at 13:18

4

The trick is actually the single ! operator there (the entire first line actually does the same thing). This will work just as well:

!function(d, w){
   ...
}(document, window);

As always I can recommend Ben Almans great article on Immediately-Invoked Function Expressions

answered Apr 23 '13 at 13:18

Daff

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thank you, i wish i could accept both answer – MimiEAM Apr 23 '13 at 15:11

strange anonymous javascript function call

2 Answers2