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for循环:循环代码块一定的次数;和java中的循环方式一样,只是输出语句而已
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For 循环
for 循环是您在希望创建循环时常会用到的工具。
下面是 for 循环的语法:
for (语句 1; 语句 2; 语句 3) { 被执行的代码块 }
<!DOCTYPE html>
<html>
<body>
<script>
//
letters=["a","b","c","d","e"];
for (var i=0;i<letters.length;i++)
{
document.write(letters[i] + "<br>");
}
</script>
</body>
</html>
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for/in 循环:循环遍历对象的属性,(NoiseDust项目中用到)
<!DOCTYPE html> <html> <body> <h3>for/in循环</h3> <button onclick="firstFunction()">For/in:循环遍历对象的("dog")属性</button> <p id = "tex1"></p> <script> function firstFunction(){ var a; var variable = ""; var dog = {fname:"雪白",age:5,phone:17709320827,adress:"西安市雁塔区510所"}; for(a in dog){ variable = variable + dog[a] + "<br>"; } document.getElementById("tex1").innerHTML = variable; } </script> </body> </html>
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while循环:当指定的条件为true执行指定的代码块
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语法
while (条件) { 需要执行的代码 }
<!DOCTYPE html>
<html>
<body>
<h3>测试循环</h3>
<button onclick="cgFunction()">点击开始循环</button>
<p id="demo2"></p>
<script>
function cgFunction(){
var x = "";
var i = 0;
while(i<5){
x = x + "第" + i + "次循环" + "<br>";
i++;
}
document.getElementById("demo2").innerHTML = x;
}
</script>
</body>
</html>
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do/while循环:是while循环的变体 ;先执行一次代码块,在判断条件是否为真之前,如果条件为真,则继续执行一次代码块
- 语法:
do
{
需要执行的代码
}
while (条件);
<!DOCTYPE html>
<html>
<body>
<p>点击下面的按钮,只要 i 小于 5 就一直循环代码块。</p>
<button onclick="myFunction()">点击这里</button>
<p id="demo"></p>
<script>
function myFunction()
{
var x="",i=0;
do
{
x=x + "The number is " + i + "<br>";
i++;
}
while (i<5)
document.getElementById("demo").innerHTML=x;
}
</script>
</body>
</html>