1、if-else

if (time<10)
{
    document.write("<b>早上好</b>");
}
else if (time>=10 && time<20)
{
    document.write("<b>今天好</b>");
}
else
{
    document.write("<b>晚上好!</b>");
}

2、switch

var d=new Date().getDay();
switch (d)
{
    case 6:
      x="今天是星期六";
      break;
    case 0:
      x="今天是星期日";
      break;
    default:
      x="期待周末";
}
document.getElementById("demo").innerHTML=x;

3、for

    <script>
        let str = 'abcdefg';
        let arrays = [1, 2, "abc"];
        //for
        for (let i = 0; i < str.length; i++) {
            console.log('for:'+str[i]);
        }
        //for of
        for (let s of str) {
            console.log('for of:'+s);
        }
        //for in
        for (let key in arrays) {
            console.log('for in:'+arrays[key]);
        }
        //forEach
        arrays.forEach(element => {
            console.log('forEach:'+element);
        });
    </script>

5、while

while

var i = 0;
while (i < names.length) {
  console.log(names[i]);
  i++;
}

do/while 循环

var i = 0;
do
{
    x=x + "The number is " + i + "<br>";
    i++;
}
while (i<5);

6、break

中止for

for (i=0;i<10;i++)
{
    if (i==3) break;
    x=x + "The number is " + i + "<br>";
}

7、continue

跳过这次for，继续下一个

for (i=0;i<=10;i++)
{
    if (i==3) continue;
    x=x + "The number is " + i + "<br>";
}

8、return

直接返回