條件語(yǔ)句

if (條件){語(yǔ)句1}else{語(yǔ)句2}

var isMale = false;
if(isMale){
    document.write('男');
}else{
    document.write('女');
}
//女

if (條件){語(yǔ)句1}else if(條件2){語(yǔ)句2}else{語(yǔ)句3}

var score = 65;
if(score > 70){
    document.write('A');
} else if(score >= 60){
    document.write('B');
} else {
    document.write('C');
}
//B

switch(表達(dá)式){
case 值1:語(yǔ)句
break;
case 值2:語(yǔ)句
break;
default:語(yǔ)句
}

var degree = 'B';
switch(degree){
    case 'A':
        document.write('優(yōu)秀');
        break;
    case 'B':
        document.write('良好');
        break;
    default:
        document.write('不合格');
}//良好

循環(huán)語(yǔ)句

while(表達(dá)式){語(yǔ)句}

var i = 1;
while(i <= 10){
    document.write(i);
    i++;
}
//12345678910

do(語(yǔ)句)while(表達(dá)式)

var i = 11;
do{
    document.write(i);
    i++;
}
while(i<=10)
//11

for(初始化;循環(huán)條件;更新表達(dá)式){語(yǔ)句}

for(var i = 1;i <= 10;i++){
    document.write(i);
}
//12345678910

break,continue

for(var i = 1; i <= 10;i++){
    if(i == 5){break;}
    document.write(i);
}
//1234
for(var i = 1; i <= 10;i++){
    if(i==5){continue;}
    document.write(i);
}
//1234678910

for(屬性名 in 對(duì)象){語(yǔ)句}

var cat = {
    name:'kitty',
    age:2,
    mew:function(){
        console.log(喵喵喵);
    }
}

for(var p in cat){
    document.write(p);
}
//name age mew

with語(yǔ)句

with(表達(dá)式){語(yǔ)句} 將當(dāng)前語(yǔ)句的代碼的作用域指向到一個(gè)特殊的對(duì)象上

var kitty = {
    age:3,
    friend:function(){
        name:'snoopy',
        age:2,
    }
}

document.write(kitty.friend.name + '\'s age is' + kitty.friend.age);
//snoopy's age is2

with(kitty.friend){
    document.write(name +  '\'s age is' + age);
}
//snoopy's age is2

異常捕獲語(yǔ)句

try{
語(yǔ)句
}catch(exception){
語(yǔ)句
}finally{
語(yǔ)句
}

try{
    document.write(notDefined);
} catch(error){
    alert(error);
} finally {
    alert('finally');
}
//ReferenceError
//finally