1whilevar num = 1//1、声明循环变量while (num<=10){//2、判断循环条件 document.write(num+"<br />")//3、执行循环体操作；num++//4、更新循环变量；} while循环()中的表达式，运算结果可以是各种类型，但是最终都会转为真假，转换规则如下。①Boolean：true为真，false为假；②String：空字符串为假，所有非空字符串为真；③Number：0为假，一切非0数字为真；④null/Undefined/NaN:全为假；⑤Object：全为真。2do-while循环while循环特点：先判断后执行；do-while循环特点：先执行再判断，即使初始条件不成立，do-while循环至少执行一次；var num = 10 do{document.write(num+"<br />")//10 9 8 7 6 5 4 3 2 1 0num-- }while(num>=0) document.write(num)//-13,for循环for (var num =1num<=10num++) {document.write(num+" <br />")//1 2 3 4 5 6 7 8 9 10 }4for-in循环 var arr = ['a', 'b', 'c', 'd'] for (let a in arr) {console.log(a)// 0 1 2 3}for (let a of arr) {console.log(a)// a b c d}JQ循环有$.each和$.map('div').each(function (i){ i就是索引值 this 表示获取遍历每一个dom对象})// 1 for循环
for (i=1i<=100i++)｛ alert (i)}
//2 while循环
var i=1
while (i<=100){
alert(i)
i++
}
//3 do while 循环
var i = 1
do{
alert(i
i++
}while(i <= 100)
//for in 和 forEach 用于数组的循环遍历
//4 for in
var arr1=[1,2,3,4,5,6,...99,100]
for (i in arr1){
alert (i)
}
//5 foreach
var arr1=[1,2,3,4,5,6,...99,100]
arr1.forEach(function(i){ alert(i)})
