Function declaration and Expression

Function declaration: directly declare a function fnname () {}; function declaration must have a method name, and the method names that appear in the expression are ignored.

Function expression: points a variable reference to a specified function or anonymous function by assigning a value. For example:

VaR fnname = function () {}; // It can be an anonymous function or a named Function

 

The following two sections of code are analyzed:

<script type="text/javascript">alert(a);function a() {return 'xx';}var a = function a() {return 'x';}alert(a);</script>

<script type="text/javascript">alert(a);function a() {return 'xx';}var a = function a() {return 'x';}alert(a);</script>

 

 

In fact, there is not much difference between the two, mainly in Var A = function a () {}, there is a difference between IE and other browsers, IE, whether it is a function expression or a function declaration, will be mentioned before scope. Why?

<script type="text/javascript">alert(a);var k = function a() {return 'x';}</script>

 

 

Other browsers will prompt a undefined (A is not defined). The rest is just a sequence problem.

 

During pre-resolution, A is function a () {} at this time, regardless of whether it is before or after var.

<script type="text/javascript">alert(a);function a() {return 'xx';}var a = '1';</script>

 

It can be understood that when parsing the <SCRIPT> code segment, the VaR is declared in advance, mentioned before the current scope, and then the function expression is pre-parsed. The definition of VaR A has nothing to do with the position of function A. When var A is executed, the reference of a is changed and it will point to the value "1"

 

 

 

To learn more about the named and anonymous functions, click the following link to view my previous articles:

Hi.baidu.com/meteoric_cry/blog/item/65f8d3c4651d64a58326ac23.html

 

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