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for循環：循環代碼塊一定的次數；和java中的循環方式一樣，只是輸出語句而已
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For 循環
for 循環是您在希望創建循環時常會用到的工具。
下面是 for 循環的語法：
for (語句 1; 語句 2; 語句 3) { 被執行的代碼塊 }
<!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 循環：循環遍歷對象的屬性，(NoiseDust項目中用到)
<!DOCTYPE html> <html> <body> <h3>for/in循環</h3> <button onclick="firstFunction()">For/in：循環遍歷對象的（"dog"）屬性</button> <p id = "tex1"></p> <script> function firstFunction(){ var a; var variable = ""; var dog = {fname:"雪白",age:5,phone:17709320827,adress:"西安市雁塔區510所"}; for(a in dog){ variable = variable + dog[a] + "<br>"; } document.getElementById("tex1").innerHTML = variable; } </script> </body> </html>
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while循環:當指定的條件爲true執行指定的代碼塊
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語法
while (條件) { 需要執行的代碼 }
<!DOCTYPE html>
<html>
<body>
<h3>測試循環</h3>
<button onclick="cgFunction()">點擊開始循環</button>
<p id="demo2"></p>
<script>
function cgFunction(){
var x = "";
var i = 0;
while(i<5){
x = x + "第" + i + "次循環" + "<br>";
i++;
}
document.getElementById("demo2").innerHTML = x;
}
</script>
</body>
</html>
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do/while循環：是while循環的變體 ；先執行一次代碼塊，在判斷條件是否爲真之前，如果條件爲真，則繼續執行一次代碼塊
- 語法：
do
{
需要執行的代碼
}
while (條件);
<!DOCTYPE html>
<html>
<body>
<p>點擊下面的按鈕，只要 i 小於 5 就一直循環代碼塊。</p>
<button onclick="myFunction()">點擊這裏</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>