JS Learning Two

1. function scope and declaration in advance

var scope = ' Global ';

function f ()

{

Console.info (scope); Output undefined

var scope = ' local ';

Console.info (scope); Output Local

}

The above code is equivalent to

function f ()

{

var scope;

Console.info (scope);

Scope = ' local ';

Console.info (scope);

}

Declare the variable in the function "ahead" to the top of the function body (but not the assignment), while the variable initialization remains in its original position

This feature is informally called "declaration ahead", and all variables declared within a function are always visible inside the function body!

2. Scope Chain

Each JS code has a scope associated with it, and this scope is a list of objects or linked lists! This set of objects defines the variable in the scope of this code!