控制语句
if-else 语句
<script>
//控制语句
//if-else格式:
var x = 1
if(x==1){
console.log("this is if")
}else if(x>1){
console.log("this is else if")
}else {
console.log("this else")
}
</script>
switch语句
<script>
//switch语句
var x = 8;
switch (x){
case 1:alert("this 1");break;
case 2:alert("this 2");break;
case 3:alert("this 3");break;
case 4:alert("this 4");break;
case 5:alert("this 5");break;
case 6:alert("this 6");break;
case 7:alert("this 7");break;
default:alert("nothing")
}
</script>
for循环语句
<script>
// for循环:for while
// 基本格式:
for(初始化;条件;增量){语句}
for(i=1;i<100;i++){
document.write(i)
document.write('<br>')
}
var x = [1,2,3,4,5,6]
for(i=0;i<x.length;i++){
document.write(x[i])
document.write('<br>')
}
//不建议使用
var x = ['a','b','c','d']
for(i in x){
document.write('this i,输出:'+i);
document.write('<br>');
document.write('this x[i],输出:'+x[i]);
document.write('<br>');
document.write('----------------------');
document.write('<br>');
}
// this i,输出:0
// this x[i],输出:a
// ----------------------
// this i,输出:1
// this x[i],输出:b
// ----------------------
// this i,输出:2
// this x[i],输出:c
// ----------------------
// this i,输出:3
// this x[i],输出:d
// ----------------------
<body>
<p>A</p>
<p>B</p>
<p>C</p>
<p>D</p>
<p>E</p>
<p>F</p>
<p>G</p>
</body>
//不建议使用的原因
var x2 = document.getElementsByTagName('p')
for(i in x2) {
document.write('this i,输出:' + i);
document.write('<br>');
document.write('this x[i],输出:' + x2[i]);
document.write('<br>');
document.write('----------------------');
document.write('<br>');
}
// this i,输出:0
// this x[i],输出:[object HTMLParagraphElement]
// ----------------------
// this i,输出:1
// this x[i],输出:[object HTMLParagraphElement]
// ----------------------
// this i,输出:2
// this x[i],输出:[object HTMLParagraphElement]
// ----------------------
// this i,输出:3
// this x[i],输出:[object HTMLParagraphElement]
// ----------------------
// this i,输出:4
// this x[i],输出:[object HTMLParagraphElement]
// ----------------------
// this i,输出:5
// this x[i],输出:[object HTMLParagraphElement]
// ----------------------
// this i,输出:6
// this x[i],输出:[object HTMLParagraphElement]
// ----------------------
// this i,输出:length
// this x[i],输出:7
// ----------------------
// this i,输出:item
// this x[i],输出:function item() { [native code] }
// ----------------------
// this i,输出:namedItem
// this x[i],输出:function namedItem() { [native code] }
</script>
while循环语句
<script>
//while 循环
var i=0;j=0;
while(i<201){
j +=i
i++;
}
document.write(j)
</script>
异常处理
<script>
//异常
//try{主程序}catch(异常){执行}finally{无论是否异常都执行}
//主动抛出异常 throw Error("xxxx")
try{
throw Error("报错了!!!")
document.write("OK")
}
catch (e) {
document.write("异常")
}
finally {
document.write("OK and OK")
}
</script>