Are “(function ( ) { } ) ( )” and “(function ( ) {

问题:

This question already has an answer here:

• Location of parenthesis for auto-executing anonymous JavaScript functions? 4 answers

Both of these code blocks below alert foo then bar. The only difference is })() and }()).

Code 1:

(function()
{
    bar = \'bar\';
    alert(\'foo\');
})();

alert(bar);

Code 2:

(function()
{
    bar = \'bar\';
    alert(\'foo\');
}());

alert(bar);

So is there any difference, apart from the syntax?

回答1:

No; they are identical

---

However, if you add new beforehand and .something afterwards, they will be different.

Code 1

new (function() {
    this.prop = 4;
}) ().prop;

This code creates a new instance of this function\'s class, then gets the prop property of the new instance.
It returns 4.

It\'s equivalent to

function MyClass() {
    this.prop = 4;
}
new MyClass().prop;

---

Code 2

new ( function() {
    return { Class: function() { } }; 
}() ).Class;

This code calls new on the Class property.
Since the parentheses for the function call are inside the outer set of parentheses, they aren\'t picked up by the new expression, and instead call the function normally, returning its return value.
The new expression parses up to the .Class and instantiates that. (the parentheses after new are optional)

It\'s equivalent to

var namespace = { Class: function() { } };

function getNamespace() { return namespace; }

new ( getNamespace() ).Class;
//Or,
new namespace.Class;

Without the parentheses around the call to getNamespace(), this would be parsed as (new getNamespace()).Class — it would call instantiate the getNamespace class and return the Class property of the new instance.

回答2:

There\'s no difference - the opening brace only serves as a syntactic hint to tell the parser that what follows is a function expression instead of a function declaration.

回答3:

There\'s no difference. Both are function expressions.

There is be a third way, too:

+function() {
    bar = \'bar\';
    alert(\'foo\');
}();

(instead of the + another operator would work, too)

The most common way is

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

though.