Javascript基本语法与C/Java非常相似，比较特殊的是，Javascript有一个for-in语句，可以用来遍历对象中的属性。
<script>
var person = {"name":"Bill Gates","age":56,"Country":"America"};
var text = "";
for (x in person){
text+=(person[x]+","); //使用person[x]取出person对象的x属性值
}
document.write(text)
</script>
代码整理自w3school：http://www.w3school.com.cn
效果图：
代码：
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<meta http-equiv="Content-Language" content="zh-cn" />
<title>Javascript 基本语句（if-else/switch/for/while/for-in/try-catch）</title>
<head>
<style>
body {background-color:#e5e5e5}
</style>
</head>
<body>
<h3>（一）if-else语句</h3>
<p>点击按钮，显示当前是上午还是下午。</p>
<button onclick = "timeNow()">确定</button>
<p id = "timeText"></p>
<script>
function timeNow(){
var x;
var time = new Date().getHours();
if (time<12){
x = "上午";
}else{
x = "下午";
}
document.getElementById("timeText").innerHTML = x;
}
</script>
<h3>（二）switch语句</h3>
<p>点击按钮，显示当前是星期几</p>
<button onclick = "weekdayNow()">确定</button>
<p id = "weekdayText"></p>
<script>
function weekdayNow(){
var x;
var time = new Date().getDay();
switch (time){
case 0:
x = "Sunday";
break;
case 1:
x = "Monday";
break;
case 2:
x = "Thesday";
break;
case 3:
x = "Wendsday";
break;
case 4:
x = "Thursday";
break;
case 5:
x = "Friday";
break;
case 6:
x = "Saturday";
break;
default:
x = "Unknown";
break;
}
document.getElementById("weekdayText").innerHTML = x;
}
</script>
<h3>（三）for语句</h3>
<script>
var cars = ["BMW","Volvo","Saab"]
for (var i =0;i<cars.length;i++){
document.write(cars[i]+"<br/>");
}
</script>
<h3>（四）for/in语句：遍历对象的属性</h3>
<script>
var person = {"name":"Bill Gates","age":56,"Country":"America"};
var text = "";
for (x in person){
text+=(person[x]+","); //使用person[x]取出person对象的x属性值
}
document.write(text)
</script>
<h3>（五）while语句</h3>
<script>
var i = 0;
while(i<5){
document.write("hello world-"+i+"<br/>");
i++;
}
</script>
<p>非boolean值作为while的条件：</p>
<script>
var cars = ["BMW","Volvo","Saab"]
var i = 0;
while(cars[i]){
document.write("cars["+i+"]="+cars[i]+",");
i++;
}
</script>
<p>注：break,continue语句与C/java完全相同</p>
<h3>（六）try-catch语句</h3>
<button onclick = "errTest()">点击按钮</button>
<script>
function errTest(){
try{
alertttt("hello");
}catch(err){
var text = "网页上有一个错误。\n错误描述：";
text+=err.message;
alert(text)
}
}
</script>
</body>
</html>