JavaScript QuickStart-ecmascript Statements

JavaScript statements (if, for, in, Do...while, while, break, continue, switch)

One, if statement

if(conditionstatement1 else Statement2

1. If ... else .....

if (2>1) {  alter ("2 greater than 1")  } else {  alert ("2 less than 1")  }

　　

2. If....else If ... else ...

<script>var A=3;var b=2if (a>b) {alert (' A greater than B ');} else if (a<b) {alert (' A is less than B ');} Else{alert (' a equals B ');} </script>

　　

Second, circular statement 1, Do...while

<script>     var a=0;    do{        a+=1;        Console.log (a);        } while (A<10) </script>

　　

2. While

<script>    b=10;    while (b>0) {        console.log (b);        b-=1;    } </script>

　　

3. For

<script> for  (var a=0;a<10;a++) {        console.log (a);    } </script>

　　

4, for...in (not recommended)

<script> var b=[1,2,3,4,5] for    (i in B) {        console.log (b[i]);    } </script>

　　

Third, switch

Syntax: Judge the expression Expresssion and the following situation, compare, and then immediately exit the loop.

switch (expression) case  value:statement;    break;  Case Value:statement;    break;  Case Value:statement;    break;  Case Value:statement;    break;  Case Value:statement;    break;  default:statement; Note: Each statement has a break keyword! In fact, the switch is the same as if, but switch uses break, the efficiency will be higher than if. The number of judgements is less than if (except in extreme cases).

　　

For example: Note: switch can perform string comparisons.

<script>    var a= ' string '    switch (a) {case        ' AAA ': Console.log (' aaa ');        break;        Case ' string ': Console.log (' I am a string ');        break;        Case ' test ': console.log (' Test ');        break;        Default:console.log (' default ');    } </script>

　　

Iv. break and Continue

The break statement can be used to jump out of this loop.

After the continue statement jumps out of the loop, the code after the loop continues to execute (if any)

Example: Continue

<script>for (var i=0;i<10;i++) {        if (i==5) {        continue;        } else{          Console.log (i);                    } </script> Results: 12346789

Break

<script>for (var i=0;i<10;i++) {        if (i==5) {break        ;        } else{          Console.log (i);                    } </script> Results: 1234

　　

Five, exception statement

try {    //This piece of code runs from top to bottom, where any one of the statements throws an exception the code block ends running}catch (e) {    ///If an exception is thrown in a try code block, the code in the catch code block is executed.    //e is a local variable that is used to point to an Error object or other thrown object}finally {//Whether or not the code in the     try is thrown (even if there is a return statement in the try code block), the finally code block is always executed. }

　　

JavaScript QuickStart-ecmascript Statements