JavaScript Advanced Programming Reading Notes (7) Statements in ECMAScript_javascript skills

if statement
Syntax:

Copy code The code is as follows:

if(condition){
statement1;
}
else{
statement2;
}

Iteration statement
1. do-while statement
Syntax:

Copy code The code is as follows:

do{
statement
}while(expression) ;

2. while statement
Syntax:

Copy code The code is as follows:

while(expression){
statement
}

　3. for statement
Syntax:

Copy code The code is as follows:

for(initialization;expression;post-loop-expression){
statement;
}

4. for-in statement
Syntax:

Copy code The code is as follows:

for(property in expression){
statement
}

　 Example:
Use the above four methods to traverse the array:

Copy code The code is as follows:

var iArr=new Array(1,2,3,4,5);
var index=0;

//do-while
do{
console.log(iArr[index]);
}while( index
//while
index=0;
while(index console.log(iArr[index-1]);
}

//for
for(index=0;indexconsole.log(iArr[index]);
}

//for- in
for(x in iArr){
console.log(iArr[x]);
}

Tagged statements
You can use the following syntax to give statements Add a label for later calls:

label:statement
For example:

start:var iCount=10;
In this example, the label start can be used later by a break statement or The continue statement calls

break statement and continue statement

Both break and continue provide tighter control over the code execution in the loop. The break statement can exit the loop immediately, while continue only exits the current loop and enters the next loop. Example:

Copy code The code is as follows:

var iNum=0;
for( var i=1;i<10;i ){
if(i%5==0){
break;
}
iNum ;
}
console.log( iNum);//4

iNum=0;
for(var i=1;i<10;i ){
if(i%5==0){
continue ;
}
iNum ;
}
console.log(iNum);//8

iNum=0;
outer://label
for( var i=0;i<10;i ){
for(var j=0;j<10;j ){
if(i==5&&j==5){
break outer;
}
iNum;
}
}
console.log(iNum);//55

iNum=0; for(var i=0;i<10;i ){
for(var j=0;j<10;j ){
if(i==5&&j==5){
continue outer ;
}
iNum ;
}
}
console.log(iNum);//95


with statement

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

Copy code The code is as follows:

with(expression){

statement
}


Usage example:

Copy code The code is as follows:

var sMessage="Hello World";

with(sMessage){
console.log(toUpperCase());//HELLO WORLD
}


switch statement

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

Copy the code The code is as follows:

switch(expression){
case value1:
statement
break;
case value2:
statement
break;
...
case valueN:
statement
break;
default:
statement
}

switch in ECMAScript can be used for strings, example:

Copy code The code is as follows:

var sColor="green";
switch(sColor){
case "red":
console.log("#FF0000");
break;
case "green":
console.log("#00FF00");//#00FF00
break;
default:
console.log("#FFFFFF");
}

Author: Tian Xingjian, self-improvement