1、循环的主要目的
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>Document</title>
<script>
for(var i = 1;i<=100;i++){
console.log("我喜欢");
}
</script>
</head>
<body>
</body>
</html>
2、js中的循环
3、for循环
3.1、for循环语法结构
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>Document</title>
<script>
for(var i = 1;i <= 100; i++){
console.log('你好吗');
}
</script>
</head>
<body>
</body>
</html>
3.2、for循环执行过程
- 1.首先执行里面的计数器变量var i = 1 .但是这句话在for里面只执行一次 index
- 2.去i<=100来判断是否满足条件,如果满足条件就去执行循环体不满足条件退出循环
- 3.最后去执行i++ i++是单 独写的代码递增第 一轮结束
- 4.接着去执行i<=100如果满足条件就去执行循环体不满足条件退出循环 第二轮
3.3、断点调试
3.4、案例:一行打印五个小星星
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>Document</title>
<script>
var str = '';
for(var i = 1;i<=5;i++){
str = str+'★';
}
console.log(str);
</script>
</head>
<body>
</body>
</html>
3.5、双重for循环
3.5.1、双重for循环概述
3.5.2、双重for循环执行过程
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>Document</title>
<script>
for(var i = 1;i <= 3;i++){
console.log('这是外层循环第' + i + '次');
for(var j = 1;j<= 3;j++){
console.log('这是内层循环第' + j + '次');
}
}
</script>
</head>
<body>
</body>
</html>
3.5.3、打印五行列的小星星
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>Document</title>
<script>
var str = '';
for(var i = 1;i <= 5; i++){
for(var j = 1;j <= 5;j++){
str = str + '★';
}
str = str +'\n'
}
console.log(str);
</script>
</head>
<body>
</body>
</html>
3.5.4、打印倒三角案例
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>Document</title>
<script>
var str = '';
for(var i = 1;i <= 10;i++){
for(var j = i;j <=10;j++){
str = str+'★';
}
str = str +'\n';
}
console.log(str);
</script>
</head>
<body>
</body>
</html>
3.5.5、打印九九乘法表案例
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>Document</title>
<script>
var str = '';
for( var i = 1;i <= 9;i++){
for(var j = 1;j <= i;j++){
str += j + 'x' + i + '=' + i * j +'\t';
}
str +='\n';
}
console.log(str);
</script>
</head>
<body>
</body>
</html>
3.6、for循环小结
4、while循环
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>Document</title>
<script>
var message = prompt('你爱我吗?');
while(message != '我爱你'){
message = prompt('你爱我吗?');
}
alert('我也爱你呀')
</script>
</head>
<body>
</body>
</html>
5、do while循环
6、循环小结
7、案例