Meaning of statement in JS

Question

Trying to figure out what this means in javascript.

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

It is isn't using jQuery, so is this just a javascript way of making this wait till document is ready to execute? Thanks.

Answer 1

This won't wait for the document to be ready, this will execute the content of the function immediately. Putting the function definition in parenthesis makes it an expression, which returns a value being the function, making it directly executable. This pattern is called an Immediately-Invoked Function Expression (IIFE) .

This is probably used in conjunction with a minifier like the Closure Compiler .

Inside the function, document is a local variable. This makes it possible for the minifier to reduce its name to a one or two character name.

Note also that all variables defined inside the function will be local : they won't leak in the global scope, which may be interesting if this is only part of the script.

Answer 2

这将创建一个接受单个参数的匿名函数，并立即将其作为document传递给document 。

Answer 3

This:

function(document) { ... } 

creates a function taking one paremeter.

This:

(function(document) { ... })

makes it (the code, not the function) a valid expression. See here .

This:

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

calls that function with document as a parameter.

It's a basic modularization pattern. In different environments you could've passed some other object instead of document, but nothing inside that function has to know bout it.

Answer 4

This is called self-executed function . It evaluates the anonymous function taking a parameter called document with that parameter passed in.