JavaScript scoped instance analysis

This article describes the JavaScript scope. Share it for your reference, as follows:

JavaScript Scope

1. JavaScript uses functions as scope

JavaScript: Using functions as scope

function func(){
  if(1==1){
    var name = 'xsk'
  }
  (name);
}
func()

2. Function scope has been created before the function is called.

JavaScript: Function scope is created in advance

function func(){
  if(1==1){
    var name = 'xsk'
  }
  (name);
}

3. The scope of the function is in the scope chain and is also created before being called.

JavaScript: Scoping chains are created in advance

Example 1:

xo = "xsk";
function func(){
  var xo = "miy"
  function inner(){
    var xo = "nn"
    (xo)
  }
  inner()
}
func()
// Output nn

Example 2:

xo = "xsk";
function func(){
  var xo = "miy"
  function inner(){
    (xo)
  }
  return inner;
}
var ret = func()
// Output miy// ret is equivalent to inner() function

Example 3:

xo = "xsk";
function func(){
  var xo = "miy"
  function inner(){
    (xo)
  }
  var xo = "tony"
  return inner;
}
var ret = func()
ret()
// Output tony

Note: Scope nested scope is called scope chain.

Note: The search variable will be preferred in the local scope and does not jump to the next level.

4. Declare local variables in the function in advance

JavaScript: Function local variable declaration in advance

Example 1:

function func(){
  (xxoo);
}
func();
// Report an error

Example 2:

function func(){
  (xxoo);
  var xxoo = 'xsk'
}
func();
// Output undefined// Function execution order, who is in front of it

(1) JavaScript When creating a function, it will automatically generate a scope chain.

(2) While generating scope, all local variables will be found to declare in advance. (var variable name)

(3) The local variables assigned to the value are undefined by default.

For more information about JavaScript, please view the special topic of this site: "Summary of common JavaScript functions techniques》、《JavaScript object-oriented tutorial》、《Summary of JavaScript Errors and Debugging Skills》、《Summary of JavaScript data structure and algorithm techniques"and"Summary of JavaScript mathematical operations usage》

I hope this article will be helpful to everyone's JavaScript programming.