Learning notes of JS variable scope and function

Scope of variable ： Limit the available range of variables , It is divided into function scope and global scope .
Function scope ：
Outside the function is the global scope – Variables can only be accessed inside functions （ The formal parameter of the function It's a local variable – It is equivalent to internally declaring the variable corresponding to the formal parameter ）.
Global scope ： Within the function is the function scope – Variables can be accessed under any scope .
~~ No keywords inside the function （var） What is declared is a global variable , But such a statement in strict mode is not standardized .

JS It's a functional programming language , A function is a code block used to complete a specific function , When a function has a return value, it can be used as the value of a variable , When there is no return value, it can be used as a tool to complete a business .
~~ When we feel that using variables to solve problems is too cumbersome and brain burning At this time, we should consider whether to draw a method To solve ： “ I feel nothing wrong, but it makes you uncomfortable ” The situation of .

Function is a Function Object of type It has two Practical built-in properties ：
(1) this
Pictured this In normal functions Pointing to window object , Global variables are also equivalent to window An attribute of an object
So in the function, we pass this You can also change the value of the global variable .

(2) arguments Express Formal parameter list information – Parameters and Corresponding value （ Class array object ）

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