Javascript ?? ???? ?? ?? ???
????? ??????
if ?
if(??){
?? ??;
}
?:
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>javascript</title>
</head>
<body>
<script type="text/javascript">
var x=5;
if(x<4){
alert('true');
}
</script>
</body>
</html>??: x? 5???. if ?? ?????. x? 4?? ??? ?? ?? ?????. ??? ????? ?? ?? ???? ????.
if...else
if(?? ){
??? ???? ?? ??
}else{
??? ???? ??? ?? ??
}
?:
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>javascript</title>
</head>
<body>
<script type="text/javascript">
var x=5;
if(x<4){
alert('true');
}else{
alert('false');
}
</script>
</body>
</html>??: x =5 ??? ????? ?????.else if....else
if(?? 1){ ? 1 ??
}else if(?? 2){
? 2 ??
}else if(?? 3){
??? 3
}else{
? ????? ???? ????. ??? ??? 4
}
?:
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>控制流程語句 if....else if....else </title>
</head>
<script type="text/javascript">
var age = 50;
if(age<=30){
document.write('青年');
}else if(age<=40){
document.write('中年');
}else if(age<=60){
document.write('中老年');
}else{
document.write('老年');
}
</script>
<body>
</body>
</html>??? ?
???(??) { ?? 1: ??? ??
?? 2: ?? ???; break;
?? 3: ??? ??;
?? :?? ???;
?:
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>流程控制語句 switch 語句 </title>
</head>
<script type="text/javascript">
var myweek=1;
switch(myweek){
case 1:document.write('學(xué)習(xí)html');break;
case 2:document.write('學(xué)習(xí)div+css');break;
case 3:document.write('學(xué)習(xí)javascript');break;
case 4:document.write('學(xué)習(xí)jquery');break;
case 5:document.write('學(xué)習(xí)php');break;
default:document.write('休息');
}
</script>
<body>
</body>
</html>??: ???? break? ?? ?????. myweek? 1? ? ?? ? ?? break? ??? ; ??? ???? ??? ???? case 1?? default?? ?? ?????. ??? ???? ????. ????? ?? ??? ???? ???
?? ?? ?????.
