1. JavaScript for/in 语句循环遍历对象的属性：
可以遍历数组，也可以遍历一个对象的所有属性
<body>
<p>点击按钮，循环遍历对象“person”的属性</p>
<button onclick="myfunction()">点击这里</button>
<p id="d1"></p>
<script>
function myfunction()
{
var txt = "";
var person = { firstname: "yoyo", lastname: "xiao", age: 34 };
for(x in person)
{
txt = txt + person[x];//把属性的值都转入一个数组
}
document.getElementById("d1").innerHTML = txt;
}
</script>
<script>
var cars = ["Audi", "BMW", "Saab","Ford"];
for (x in cars)
{
document.write(cars[x]+"</br>");
}
</script>
</body>
2. For循环
for (语句 1; 语句 2; 语句 3) { 被执行的代码块 }
3. While循环
while(condition)
{
代码块
}
do
{
} while(condition)
4. break: 跳出循环
continue: 跳出当次循环