ES10知识点

1：flat 降维 flatMap

const arr = [
    [1, 2, 3],
    [20],
    [
        [21, 22],
        [23, 24]
    ],
    [90]
]
console.log(arr);
// flat的使用 默认降一个维度
console.log(arr.flat());
//降二维
console.log(arr.flat(2));
//flatMap的使用
const num = [10, 20, 30]
const nums = num.flatMap(item => {
    return item * 2
})
const nums2 = num.map(item => {
    return item * 2
})
console.log(nums, nums2);
//flatMap的应用场景
const message = ["hello world", "hey tyy", "happy heathy"]
const words = message.flatMap(item => {
    return item.split(" ")
})
//使用map得不到想要的结果需要再降维
const words2 = message.map(item => {
    return item.split(" ")
})
console.log(words);
console.log(words2);

 

 

 2:Object的fromEntries就是Entries的反向操作

const obj = {
    name: 'tyy',
    age: 20
}
const objEntries = Object.entries(obj)
console.log(objEntries);
console.log(Object.fromEntries(objEntries));

 

 

 应用场景：

   //应用场景
const queryString = 'name=tyy&age=20&heitght=1.60'
const queryParms = new URLSearchParams(queryString)
console.log(queryParms);
for (const param of queryParms) {
    console.log(param);
}
const pramobj = Object.fromEntries(queryParms)
console.log(pramobj);

 

 

 3：trim 去除空格

const message = "     hello world  "
console.log(message);
console.log(message.trim());
console.log(message.trimStart());
console.log(message.trimEnd());

 

 

 4：Symbol description

console.log(Symbol('').description);
console.log(Symbol().description);