$在“ jQuery（function（$）{…}}”中的符号如何表示jQuery？

Question

below, it says $ sign refers to jQuery. i need help understand how?

jQuery(function($){
    // Here `$` refers to jQuery
});

Answer 1

When you pass a function to jQuery like this:

jQuery(function() {
    ...
});

It's the same as using jQuery's "document ready" handler:

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

however the argument passed to that function is actually the global jQuery object itself - it's just that most such handlers never use that parameter. Hence the real signature is this:

jQuery(document).ready(function($) {
    ...
});

so, within that function $ is a local alias to the global jQuery object. The variable name could be anything you wanted, but $ is a popular alias for jQuery , and the default global alias unless you call jQuery.noConflict() .

This is described in more detail in the paragraph " Aliasing the jQuery Namespace " at http://api.jquery.com/ready/

Answer 2

That function is a so called allonymous function where jQuery runs that allonymous function with the first parameter this.

So just for understanding it makes something like this:

function jQuery(xx) {
    xx(this);
}

Answer 3

Just an example for show you how is it possibile

function externalLibrary(b) {
    if(typeof b === 'function') {
        b(externalLibrary);
    }else {
        // other stuff
    }

}

var myFunc = function(aliasOfExternalLibrary) {
    // here aliasOfExternalLibrary is a reference to externalLibrary
}
externalLibrary( myFunc );

jQuery do the same (in one more complex system)