++的前置与后置
let a1 = 1
let b1 = 2
let c1 = b1 + a1++
console.log(a1, b1, c1);//2,2,3
let a2 = 1
let b2 = 2
let c2 = b2 + ++a2
console.log(a2, b2, c2);//2,2,4
说明:
- 后置是先计算再++
- 前置是先++再计算
短路运算
let a = 0;
let b = 1;
let c = a || b;
console.log(c);//1
利用这个原理,我们可以简化一些函数
let sex = prompt('您的性别?')
if (!sex){
sex="保密"
}
console.log(sex);
=>
let sex = prompt('您的性别?') || "保密"
console.log(sex);
再比如:
/*function judge(num) {
if (num % 2 === 0) {
return "偶数"
} else {
return "奇数"
}
}*/
function judge(num) {
return num % 2 === 0 && "偶数" || "奇数"
//return num % 2 === 0 ? "偶数" : "奇数"
}
console.log(judge(2));//偶数
说明: 可以用来简化if
条件判断语句,具体如下面这段伪代码
if (flag) {
//...do something
} else {
//...do something
}
简化为 =>
flag && {...do someting} || {...do someting}