Jquery is really not difficult ~ First basic programming knowledge

ArticleDirectory

• Preface
• Variable
• Function
• Condition Statement
• Loop statement

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Preface

Before talking about jquery, let's take a look at the basic knowledge issues in JavaScript (later referred to as JS) language.Programming LanguageThe basic knowledge is similar to that of variables, functions, conditional statement blocks, and cyclic statement blocks. However, each language is different in terms of writing, for example, when defining variables in JS, you must use VaR to declare local variables. For weak language JavaScript, you can also do this without adding var, however, if you do not add the variable, you will consider it as a global variable.

Variable

InProgramThe value can be changed during running (haha, as defined in the book more than 10 years ago)

VaRPeople;//Declare a variable named PeopleVaRPeople ="Good boy";//Assign a value to a variable while declaring it. The browser automatically interprets it as a variable of the variable type.VaRAge =23;//Declares a local variable of the integer type.Age =30;//Declares a global variable of the integer type. During program execution, it will not be released.
 

Function

To implement a functionCodeBlocks are organized together to form a whole. We call it a function, which can greatly reduce the amount of code repetition and make the program clearer.

   // Standard writing  Funciton hellofun () {alert (  "  Hellow world  "  )}  //  Variable format    VaR Hellofun = Function () {alert (  "  Hellow world  "  )}  //  A function can have parameters, but it is of a weak type.  VaR Hellofun = Function (MSG) {alert (MSG );}  //  Function call Hellofun ( "  Hello World  " );

Condition Statement

If there are multiple results for one thing, the condition statement will appear. If the condition is fixed with several values, you can use switch. Otherwise, you can use if... else to check the code.

 //  Switch instance  VaR Inputnumber = Document. getelementbyid ( "  Type  " ). Value;  Switch  (Inputnumber ){  Case   1  : Alert (  "  Type 1  "  );  Break  ;  Case   2  : Alert (  "  Type 2  " );  Break  ;  Case   3  : Alert (  "  Type 3  "  );  Break  ;  Default  : Alert (  "  Throw new exception ()  "  ); Break  ;}  //  If instance  VaR Inputage = Document. getelementbyid ( "  Age  "  ). Value;  If (Inputage> 1 & Inputage < 18  ) {Alert (  "  Minor  " );}  Else   If (Inputage> = 18 & Inputage < 70  ) {Alert (  "  Adult  "  );}  Else   If (Inputage> = 70  ) {Alert (  "  Elderly "  )}  Else  {Alert (  "  Incorrect form filling  "  );} 

Loop statement

That is, when a condition is attached, a code block is repeatedly executed. We can use while, for, and so on.

//For LoopVaRArr = [1,2,3]For(VaRI =0, J = arr. length; I <j; I ++) {Console. Log (ARR [I]);//The result is displayed on the Firefox console.}
 

In fact, in the JS world, the execution performance of code is also very exquisite. Our Writing Performance in the for statement is not wrong, but if it is written below, the performance will decrease, because every time

The length of the ARR is evaluated.

//For LoopVaRArr = [1,2,3]For(VaRI =0; I <arr. length; I ++) {Console. Log (ARR [I]);//Poor performance}
 

Now, I will write down the basic JS programming knowledge here. Starting from the next time, I will introduce jquery-related knowledge. Thank you for reading this article!

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