Everest -3.JS manipulation statements: determining, loop

JS manipulation statements: determining, loop

Condition holds what? Not established what?

• if /else if/else

   if(条件){
      条件成立执行
    } else if(条件2){
      条件2成立执行
    } ....
    else{
      以上条件都不成立
    }

• Ternary operator

条件? 条件成立事件 : 不成立处理的事情
1.如果处理的事情比较多，我们用括号抱起来，每一件事情用逗号分隔，
2.如果不需要处理事情，可以使用 null/undefined 站位

let a = 10;
a > 0 && a < 20 ? (a++ , console.log(a)) : null;

if (a > 0 && a < 20) {
a++;
console.log(a);
}

-----------------------------------------------------------

a > 0 ? (a < 10 ? a++ : a--) : (a > -10 ? a += 2 : null);

/*   
    if (a > 0) {
        if (a < 10) {
            a++;
        } else {
            a--;
        }
    } else {
        if (a > -10) {
            a += 2;
        }
    } */

• switch case

不加break，当前条件成立执行完成后，后面条件不论是否成立都要执行，直到遇到break为止(不加beak 可以实现变量在某些值的情况下做相同的事情)
switch 里面的case 情况的比较用的都是 '===' 绝对相等
if里面情况比较用的的是 '==' 相等
   let a = 1;
   switch (a) {
       case 1: console.log("哈哈");
       case 5: console.log('嘿嘿5');
           break;
       case 9: console.log('滴滴9');
           break;
       case 10: console.log('嘻嘻10');
           break;
       default: console.log('哦豁');//以上都不成立
   }

---

#### === vs ==

== Equal to: if the data value is not the same type, certainly not different types, the default is first converted to the same type, and then compare '5' == 5 => true

=== absolutely equal: If the type is not the same, certainly not equal, the default will not convert the data type '5' === 5 => false

Project in order to ensure that the business cautiously recommended ===;

---

cycle

Repeat the cycle is to do certain things

continue: the end of the current round loop (continue behind the code is not executed) proceed to the next round

break: the forced end of the whole cycle (after the code execution is BREAK) and the whole cycle is ended what is not dry

• for loop

  /*
  1.创建循环初始值
  2.设置 循环执行的条件
  3.条件成立执行循环体中的内容
  4.当前循环结束执行步长累计操作
  */

• for in loop

• for of loop

• while loop

• do while loop

Is equal to: If the left and right sides of the different types of data values, the default is first converted to the same type, then comparing the