Why is this JavaScript/jQuery Syntax Used: (function( window, undefined ) { })(window)
In jQuery 1.4, the source code is encapsulated in a peculiar syntax:
(function( window, undefined ) {
//All the JQuery code here
...
})(window);
Breaking Down the Syntax:
- The (function(...) { }) portion creates an anonymous function.
- window is passed as a parameter, representing the global scope.
- undefined is also passed as a parameter and is used to ensure that the undefined variable is purely local within the function.
Purpose of the Undefined Parameter:
The purpose of the undefined parameter is to create a local undefined variable within the function. Normally, undefined is a global variable. By defining it within the function, any attempts to reassign undefined will be limited to the function's scope, preventing unintended global modifications.
Purpose of the Window Parameter:
The window parameter is passed for performance optimization. JavaScript searches for variables in local scopes before global scopes. By passing window as a parameter, it is made locally available, reducing the time it takes to look up variables.
Explanation:
This syntax helps jQuery isolate its code from the global scope and achieve better performance by minimizing the search time for variables. The function ensures that the undefined variable is purely local, preventing any global conflicts, while the window parameter optimizes variable lookup and execution speed.
The above is the detailed content of Why Does jQuery Use `(function(window, undefined){})(window);`?. For more information, please follow other related articles on the PHP Chinese website!
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