Examples of variable and function declaration in JavaScript

Examples of variable and function declaration in JavaScript
As shown in the following example:
(You can use the Chrome browser, and then right-click F12/or review the elements. Call out the developer tool and enter the console)
(TIPS: Shift + Enter in the console can be used to wrap code in the middle)

Var name = "xiaoming"; (function () {var name = name | "Xiao Zhang"; console.info (name) ;}) (); // Xiao Zhang (function () {name = name | "Xiao Zhang"; console.info (name) ;}) (); // xiaoming (function () {var name2 = name; var name = name | "Xiao Zhang"; console.info (name, name2) ;}) (); // Xiao Zhang undefined

The execution is as follows:



Explanation:
In JavaScript,

Function xxx () {// a bunch of code... //... var name2 = name; var name = name | "Xiao Zhang"; // a bunch of code}

The execution is equivalent to the following:

Function xxx () {var name2 = undefined; var name = undefined; // other var values will also be pushed to the very beginning. // a bunch of code... //... name2 = name; name = name | "Xiao Zhang"; // a bunch of code}

You can also refer to the Bootstrap Chinese network tutorial How to declare variables and functions in JavaScript (hoist)

Date:

Author: Tie an (http://blog.csdn.net/renfufei)

Urgent. Question about javascript variable declaration?

First:

<Script language = "javascript">
Var kk = "123 ";
Ss = "789 ";
Document. write (kk + '<br>' + ss );
</Script>

The declared variable is written in this way var kk = "123", ss = "789 ";
Now I write the ss to the next line. Isn't the ss a variable declared by var at this time?

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A:
Var kk = "123"; // check whether the error is "; (semicolon)". The correct one is comma (,);
Correct definition method:
Var kk = "123", // note that comma is used here
Ss = "789 ",
Aa = "11 ",
Bb = "22 ",
Cc = "33 ",
// Infinite variables can be defined.
Xx = "77 ",
Yy = "88 ",
Zz = "99"; // a semicolon is used only when the last one arrives, and a semicolon must be used;

Second:

<Script language = "javascript">
Var kk = "123 ";
Kk = "789 ";
Document. write (kk + '<br>' + ss );
</Script>

Originally, I wrote var kk = "123", kk = "789 ";
Now I have changed kk = "789" to the next line. Is kk declared again with var in the same variable?
**************************************** *************
A:
First, the kk value defined here is the same as what you think: 789, And the syntax error in "first" is also displayed here.

Third:
<Script language = "javascript">
Var
Kk = "123 ";
Ss = "789 ";
Document. write (kk + '<br>' + ss );
</Script>
If I write a single line of var, can kk and ss be declared?
**************************************** *************
A:
Yes, it's exactly the same as what you think. Here we declare both kk and ss variables;
()... Remaining full text>

Function declaration in javascript

First standard function declaration
The second one is similar to the first one, but it is used as an anonymous function value-assigned variable. In terms of semantics, however, the final effect is the same. A func2 variable name will be generated in the current context.
Third, I rarely use this method, but it should also work. It is actually equivalent to var func3, func4; func3 = func4 = function (){}
The fourth is to use the Function constructor. This constructor uses a string to construct a Function dynamically. For example, you can concatenate a Function using a string, for example, new Function ("alert var" + varName + "+ var" + varName2) is used to pre-compile javascript with high performance. This method is often used by the javascript template engine.