Examples of early declaration of variables or functions in JavaScript_javascript tips

As shown in the title, look at the example below.

(You can use the Chrome browser, then F12/or right-click, inspect the element. Call up the developer tools and enter the console input)
(Usage tips: Shift Enter can break the code midway during console input)

Copy code The code is as follows:

var name = "xiaoming";

(function(){
var name = name || "小张";
console.info(name);
})();// Xiao Zhang

(function(){
name = name || "小张";
console.info(name);
})(); // xiaoming

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

The screenshot during execution is as follows:

The explanation is as follows:

In JavaScript.

Copy code The code is as follows:

function xxx(){
// A bunch of code...
// ...
var name2 = name;
var name = name || "小张";
// A bunch of code
}

When executed, it will become this equivalent form:

Copy code The code is as follows:

function xxx(){
var name2 = undefined;
var name = undefined;
// Other vars will also be advanced to the beginning
// A bunch of code...
// ...
name2 = name;
name = name || "小张";
// A bunch of code
}