前端js小技巧篇

1:键值打印

let num = {
        age:'123',
        name:'joe',
        height:'196'
    }
    console.log({num}); //变量包装，可以同时打印出变量名和变量值

*可以打印出属性名和值，便于在复杂的业务中找到打印结果

2.&& ?? ?.

//1.&&
let num = 6
//if(num > 5){console.log('执行')}
//简化后：
num > 5 && console.log('执行');

//2.??
let obj = {
  value:null
}
let objs = obj.value ?? '100'
//*null值判断符，当左边为null或者为undefined才返回右边的值

//3.?.
let street = user.address && user.address.street;
//简化后：
let street = user.address?.street;
//*?.也叫链式判断运算符，逐层判断左边是否为null或者undefined,如果是就不在继续往下运算，如果不是则返回右边的值

3.includes

let arrays = [8,9,10,11]
    let num = 8
    if(arrays.includes(num)){
        console.log('ok');
     }
//*如果数组中存在我想查询的值，则执行后面的步骤

4.字符串转为数字

let num = '44'
console.log(+num)

5.对象：object.hasOwn

let obj = {
        name:'join',
        age:'16'
    }
    console.log(Object.hasOwn(obj,'name'));
//*查询对象中是否有某个键，有则返回true

6..at

let arr = [1,2,3,4]
console.log(arr.at(-1));
console.log(arr.at(0))
//*查询数组中某一项下标的值，-1是最后一位，0是第一位