jQuery变量阴影

Question

There is strange pattern in jQuery:

var jQuery = (function() {

// Define a local copy of jQuery
var jQuery = function( selector, context ) {
 ...
return jQuery;

})();

What is the practical reason for this? Why not just expose the inner jQuery function? Is it only for name clashes in the inner jQuery and outer jQuery since both are in closures.

Answer 1

jQuery.noConflict(true) removes the global name for jQuery. However, it would be impossible to program the rest of the jQuery library without using some name for the object, so a local, non-exposed name needs to be used. For convenience, they redefine jQuery as a variable in the scope of the anonymous function.

Answer 2

The pattern itself is called module pattern. It´s not specific for jQuery and it´s not strange but very helpful. It allows for hiding of the objects state and implementation. It also allows for priveleged methods (public methods with access to private data) and other good design principles.