"15" JavaScript

Javascript

A programming language that is compiled and run by the browser

First, JS existence form

• JS file
• HTML in the current code block

Placement: The bottom of the body tag, first display page content, and then load JS effect, prevent loading JS effect time too long affect the page display.

Second, JS variable

Local variable: var a = 123;

Global variables: a = 123; *****

PS Application Method: Variables are first set to local variables, need to set the global variables separately

<script>
    Define function    F1 () {        var i = 123;  local variable        i = 123;    global variable    }     F1 ();     Alert (i);</script>

Third, JS data type

Primitive Type: Number, String, Boolean

Object type: Array, dictionary

1. Numbers (number)

Transformation:

parseint (): Converts a value to a number, or Nan if unsuccessful

Parsefloat () Converts a value to a floating-point number, or Nan if unsuccessful

2. Strings (String)

Racing Lights

<! DOCTYPE html>
3. Boolean
= = equals, Comparison value
= = = equals, comparison type and value
! = does not equal
!== not equal to, comparison type and value
&& and
|| Or
4. Arrays
Obj.splice (Start, DeleteCount, value, ...) inserting, deleting, or replacing elements of an array
Obj.join (Sep)
Python
JavaScript:li.join "_"
Iv. Other
1.JSON serialization

 
 

  
  
 
   
Json.stringify (obj) serialization
 
   
Json.parse (str) anti-sequence China
 
  
 
 
2. Escaping

 
 

  
  
 
   
decodeURI () characters that are not escaped from the URL
 
   
decodeURIComponent () non-escaped characters in the URI component
 
   
encodeURI () escape character in Uri
 
   
encodeURIComponent () escapes the characters in the URI component
 
   
Escape () escapes the string
 
   
Unescape () to escape string decoding
 
   
Urierror is thrown by URL encoding and decoding methods
 
  
 
 
V. Statements and exceptions
1. Conditional statements
If
Switch
2. Looping statements
Mode one: For
var li = [11,22,33,44]; // The first type for  for (var i = 0; i < 4;i++) {    Console.log (i, Li[i]);}
Way two: for can handle dictionary
var li = [11,22,33,44//  second for, index, can handle dictionary for (var  in li) {     console.log (Item,li[item])}
Way three: While
3. Exception Handling
try{}
catch (e) {}
finally{}
Active Throw exception: throw new Error (' xxxxx ')
Python throws Exception: Raise Exception (XXXXX)
Vi. functions
1. Basic functions
Common functions
function func (ARG) {     return true;}
anonymous functions
Function (ARG) {     return ' Tony ';};
Self-executing functions
(function (ARG)) {     alert (arg);} (123)

# for Encapsulation
2.JavaScript Scopes

 
 

  
  
 
   
No block-level scopes in JavaScript
 
   
JavaScript takes function scope
 
   
The scope chain of JavaScript
 
   
JavaScript is created before the scope chain is executed
 
  
 
 
"15" JavaScript