JavaScript 支持不同类型的循环: for - 循环代码块一定的次数 for/in - 循环遍历对象的属性 while - 当指定的条件为 true 时循环指定的代码块 do/while - 同样当指定的条件为 true 时循环指定的代码块
<!DOCTYPE html> <html> <head> <meta charset="utf-8"> <title>菜鸟教程(runoob.com)</title> </head> <body> <p>点击按钮循环代码5次。</p> <button onclick="myFunction()">点击这里</button> <p id="demo"></p> <script> function myFunction(){ var x=""; for (var i=0;i<5;i++){ x=x + "该数字为 " + i + "<br>"; } document.getElementById("demo").innerHTML=x; } </script> </body> </html>
同时您还可以省略语句 1(比如在循环开始前已经设置了值时): <!DOCTYPE html> <html> <head> <meta charset="utf-8"> <title>菜鸟教程(runoob.com)</title> </head> <body> <script> cars=["BMW","Volvo","Saab","Ford"]; var i=2,len=cars.length; for (; i<len; i++){ document.write(cars[i] + "<br>"); } </script> </body> </html>
JavaScript for/in 语句循环遍历对象的属性: <!DOCTYPE html> <html> <head> <meta charset="utf-8"> <title>菜鸟教程(runoob.com)</title> </head> <body> <p>点击下面的按钮,循环遍历对象 "person" 的属性。</p> <button onclick="myFunction()">点击这里</button> <p id="demo"></p> <script> function myFunction(){ var x; var txt=""; var person={fname:"Bill",lname:"Gates",age:56}; for (x in person){ txt=txt + person[x]; } document.getElementById("demo").innerHTML=txt; } </script> </body> </html>