Javascript advanced programming (7): Statements in ecmascript

If statement

Syntax:

 
1 If(Condition ){
2Statement1;
3}
4 Else{
5Statement2;
6}
 

Iteration statement

1. Do-while statement

Syntax:

 
1 Do{
2Statement
3}While(Expression );
 

2. While statement

Syntax:

1 While(Expression ){
2Statement
3}
 

3. For statement

Syntax:

 
1 For(Initialization; expression; post-loop-expression ){
2Statement;
3}
 

4. For-in statement

Syntax:

 
1 For(PropertyInExpression ){
2Statement
3}
 

Example:

Use the above four methods to traverse the array:

 1  VaR Iarr = New Array (1, 2, 3, 4, 5 );
 2   VaR Index = 0;
 3  
 4   //  Do-while  
  5   Do {
 6 Console. Log (iarr [Index]);
 7 }While (++ Index <iarr. Length );
 8  
 9   //  While  
  10 Index = 0;
 11   While (Index ++ <iarr. Length ){
 12 Console. Log (iarr [index-1]);
 13 }
 14  
 15  //  For  
  16   For (Index = 0; index <iarr. length; index ++ ){
 17 Console. Log (iarr [Index]);
 18 }
 19  
 20   //  For-in  
  21   For (XIn Iarr ){
 22 Console. Log (iarr [x]);
 23 }

Tagged statements

You can use the following syntax to add labels to statements for future calls:

 
1Label: Statement
 

For example:

 
1Start:VaRIcount = 10;
 

In this example, the tag start can be called by subsequent break statements or continue statements.

Break and continue statements

Both Break and continueCodeExecution provides stricter control. The break statement can immediately exit the loop, while the continue only exits the current loop and enters the next loop. Example:

 1   VaR Inum = 0;
2   For ( VaR I = 1; I <10; I ++ ){
 3       If (I % 5 = 0 ){
 4           Break ;
 5 }
 6 Inum ++;
 7 }
 8 Console. Log (inum ); //  4 
  9  
 10 Inum = 0;
 11   For ( VaR I = 1; I <10; I ++ ){
 12       If (I % 5 = 0 ){
 13           Continue ;
 14 }
 15 Inum ++;
 16 }
 17 Console. Log (inum ); //  8  
  18  
 19 Inum = 0;
 20 Outer: // tag
 21   For ( VaR I = 0; I <10; I ++ ){
 22       For ( VaR J = 0; j <10; j ++ ){
 23           If (I = 5 & J = 5 ){
 24               Break Outer;
 25 }
 26 Inum ++;
 27 }
 28 }
 29 Console. Log (inum ); //  55  
 30  
 31 Inum = 0;
 32 Outer: // tag
 33   For ( VaR I = 0; I <10; I ++ ){
 34       For ( VaR J = 0; j <10; j ++ ){
 35           If (I = 5 & J = 5 ){
 36               Continue Outer;
 37 }
 38 Inum ++;
 39 }
 40 }
 41 Console. Log (inum ); //  95 

With statement

The with statement is used to set the scope of code in a specific object. Its syntax is as follows:

 
1 With(Expression ){
2Statement
3}
 

Usage example:

1 VaRSmessage = "Hello World ";
2 With(Smessage ){
3Console. Log (touppercase ());//Hello World
4}
 

Switch statement

The sister statement of the IF statement is the switch statement. The switch syntax is as follows:

 1   Switch (Expression ){
 2       Case Value1:
 3 Statement
4           Break ;
 5       Case Value2:
 6 Statement
 7           Break ;
 8 ...
 9       Case Valuen:
 10 Statement
 11           Break ;
 12       Default :
 13 Statement
 14 }

The switch in ecmascript can be used as a string, for example:

 1   VaR Scolor = "green ";
 2   Switch (Scolor ){
 3       Case "Red ":
 4 Console. Log ("# ff0000 ");
5           Break ;
 6       Case "Green ":
 7 Console. Log ("#00ff00 "); //  #00ff00  
  8           Break ;
 9       Default :
 10 Console. Log ("# ffffff ");
11 }