在JavaScript中自我声明匿名函数之前的美元符号？

Question

What is the difference between these two:

$(function () {
    // do stuff
});

AND

(function () {
    // do stuff
})();

Answer 1

The first uses jQuery to bind a function to the document.ready event. The second declares and immediately executes a function.

Answer 2

$(function() {}); is a jQuery shortcut for

 $(document).ready(function() { 
     /* Handler for .ready() called. */ 
 });

While (function() {})(); is a instantly invoked function expression, or IIFE. This means that its an expression (not a statement) and it is invoked instantly after it is created.

Answer 3

一个是jquery $(document).ready函数，另一个是调用自身的匿名函数。

Answer 4

They are both anonymous functions, but (function(){})() is called immediately, and $(function(){}) is called when the document is ready.

jQuery works something like this.

window.jQuery = window.$ = function(arg) {
    if (typeof arg == 'function') {
        // call arg() when document is ready
    } else {
       // do other magics
    }
}

So you're just calling the jQuery function and passing in a function, which will be called on document ready.

The 'Self-executing anonymous function' is the same as doing this.

function a(){
    // do stuff
}
a();

The only difference is that you are not polluting the global namespace.

Answer 5

$(function () {
    // It will invoked after document is ready
});

This function execution once documents get ready mean, the whole HTML should get loaded before its execution but in the second case, the function invoked instantly after it is created.

(function () {
    // It will invoked instantly after it is created
})();