Can't get some JS syntax

Question

file.js:

(function(m) {
    //some
    //code
    //here
}(m))

I can't get what does this construction mean?

That is [IIFE](http://stackoverflow.com/questions/8228281/what-is-the-function-construct-in-javascript) — Dhaval Marthak, Jun 19 '15 at 07:52

score 3 · Answer 1 · answered Jun 19 '15 at 07:53

3

That code defines a function inline and it immediately executes it.

Think about it by substituting the function for a variable:

(function(m) {
    //some
    //code
    //here
}(m))

Then that's the same as:

var f = function(m) {
    //some
    //code
    //here
}
(f(x))

But without having to define the f.

answered Jun 19 '15 at 07:53

ssice

But why they use () surround function call? – sector119 Jun 19 '15 at 07:56
2

@sector119: Because without them, the parser is in a state where seeing the keyword `function` will start a function *declaration*. To invoke it immediately, we need the parser to start a function *expression*, so we use parens (or a `+`, or a `!`, etc.) to put the parser in a state where only an expression, not a declaration, is valid. [More in this answer.](http://stackoverflow.com/a/13341710/157247) – T.J. Crowder Jun 19 '15 at 07:57
1

The extra `()` makes it an expression rather than just a function definition which is required for it to work as desired. – jfriend00 Jun 19 '15 at 07:57

1 Answers1