JS series: JS programming language

1. Programming language
html+css markup language
js: lightweight interactive language - > full stack programming language

  • object-oriented:

    • C++
    • JAVA
    • PHP
    • C# (.net doc)
    • JS
  • Process oriented

    • C
java has nothing to do with javascript

2. What parts does JS learn?

  • ECMAScript(es)
  • DOM: Document Object Model
    API (properties and methods) allows JS to get dom elements in the operation page
  • BOM: browser object model. Provide various APIs for js to operate browser

3. Variable
It is not a specific value, but a container for storing the specific value. The value can be changed.
Based on es syntax specification, js creates variables

  • var (es3)
  • function (es3) creates a function, which is also a variable, and the stored value is a function type
  • let (es6) create variables
  • const (es6)
  • import module specification based on es6 to export required information
  • Class create a class based on es6

      var   [Variable name]=Value; var num = 12;
      let   [Variable name]=Value;
      const [Variable name]=Value;
      function Function name (){    function Fn(){}
      }
      ...
      var n = 13;
      n= 14;
      alert(n+10); =>Pop it out 24, now n For and on behalf of 14;
    
      const m = 100;
      m = 200; =>Assign to constant( var let const Define the difference between variables)

Create variable name: more semantic add/ create / insert / delete(del) / update /remove(rm) / info / detali

  • Case sensitive
  • Follow the hump writing method, and name according to numbers, letters, underscores, $(numbers cannot be used as the beginning); English naming words are spelled into a complete name, the first word is lowercase, and other meaningful words are capitalized
  • Can't use (special meaning) keyword and (may become keyword in the future) reserved word

    var n = 12;
    var N = 13;//=>Two n's are not the same variable
    var studentInfo / student_info / _studentInfo (_Underline first, all public variables)
    $studentInfo (General storage jquery element)
  • Basic data type

    • number boolean null string undefined
  • Reference data type

    • object

      • Common object {} array object [] regular object / ^ / Date object date
    • function
  • Unique value of special type symbol added in es6

       var n = 13;//=>There is a special value NaN(not a number) in the number 0-13 12.2, indicating that it is not a valid number, but it belongs to the number type
       var s = '';//=>The quotation marks of '12' {} are all composed of 0 or more characters
    
       var b = true;=>Boolean 2 values true and false false
       [Reference data type]
       var o = {name : 'Mount Everest',age: 9};//=>Normal objects: braces wrap multiple sets of attributes and attribute values {} empty objects
       var ary = [12 ,23,24,25] ;//=>Multiple items wrapped in brackets are arrays, 0 to multiple items [] are empty arrays
       var reg = /-?(\d|([1-9]\d+))(\.\d+)?/g ;=>A complete regularity consisting of metacharacters // It's not regular, it's a single line comment
       function fn (){
    
       }
       symbel Created with unique values
       var a = Symbel ('Mount Everest');=>Symbol('Mount Everest')  Symbol Not a string
       var b = Symbel ('Mount Everest');                  "Symbol" Is a string
        a==b;  ->false
  • [code if run]

    • Browser kernel to render parsing
    • Run v8 engine based rendering based on node and parse js tool / / run the current file based on node through cmd
    • [output result]
    • Alert: pop up mode browser prompt box window.alert Full name output results are all converted to strings
    • alert(1+1);=> '2'
  alert ([12,23]);=>'12,23' 
  [12,23].toString() =>"12,23"
  alert({name: 'xxx'}); =>'[oject Object]' object toString The result is object object What is the object?

  - confirm : Confirmation prompt box with confirmation and Cancel buttons
  ```javascript
     var flag = confirm('Are you sure you want to exit?');
        if(flag){
          //> flag:true  Event confirmation button clicked by the client
        } else {
          //> flag:false  Click the Cancel button
        }
   ```
   - prompt :stay confirm Add input box on the basis
    var num =12;
    var flag =prompt(num);
    alert(flag);
    - console.log: Enter the log in the browser console( fn+f12)
       /* Shortcut key: num.log  TAB*/
        + Elements:Display and modify elements and styles in the current page
        + consloe :Console, js In code.log Output here, or write directly js
        + console.dir : than log Output more details (when outputting object data values)
        - console.table: hold json Data output in tabular form
        - console.log(' Normal output~ ');
        console.warn(' Output warning! ');
        console.error(' Output error!!! ');

        

Tags: Javascript Programming Java PHP

Posted on Sun, 07 Jun 2020 05:21:11 -0400 by monkey_05_06