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JavaScript Basics (1)

Source: Internet
Author: User
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1. Preface
    • ECMAScript explanation, used to explain JS code
    • DOM Document Object model, the browser needs to render the DOM tree when it is displayed
    • BOM Browser object model, you can control the browser behavior, code compatibility is poor
2. Basic type

Number type: var a = 12;

String: var a = "string";

function Type: var a = function ()

Object type: var a = document

Boolean type: var a = Boolean

The type of a variable is determined by its assignment.

3. Type conversion
    • Show transformations
<!DOCTYPE HTML><HTML><Head>    <title>Sum</title>    <Scripttype= "Text/javascript">window.onload= function (){               varobtn=document.getElementById ('btn'); Obtn.onclick= function (){            varOINPUT1=document.getElementById ('INPUT1'); varOInput2=document.getElementById ('Input2'); varvalue1=parseint (oinput1.value);//Convert a string to an int            varvalue2=parseint (Oinput2.value); if(!IsNaN (value1)&& !IsNaN (value2))//determine if a variable is a numeric typeAlert (value2+value1); }    }    </Script></Head><Body>    <inputtype= "text"ID= "INPUT1">    <inputtype= "text"ID= "Input2">    <ButtonID= "BTN"type= "button">Sum</Button></Body></HTML>
    • Implicit type conversions

= = value Equal is True

= = = Type is equal and the value equals True

+ String Connector/number addition

-Converts a string to a numeric subtraction operation

4. Scope of variables
    • Closures: Child functions can access variables in the parent function
      function A () {     var temp =1;     Function B () {           temp = 2;     }    }
    • Variable Naming conventions

　　

5.json parsing
    • Single Access JSON
<!DOCTYPE HTML><HTML><Head>    <title>Json</title>    <Scripttype= "Text/javascript">    varJSON={A: A, B:"SSS", C:12.4};    alert (JSON.A); Alert (json['b']); </Script></Head><Body></Body></HTML>
    • Iterate through JSON
<!DOCTYPE HTML><HTML><Head>    <title>Json</title>    <Scripttype= "Text/javascript">    varJSON={A: A, B:"SSS", C:12.4}; //TMP is the key, Json[tmp] is the value     for(vartmpinchJSON) alert (json[tmp]); </Script></Head><Body></Body></HTML>

JavaScript Basics (1)

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