js 数组 对象学习操作

Array.from 达到map的效果

let arr=[
  {name:'小智1',age:23},
  {name:'小智2',age:13},
  {name:'小智3',age:43},
  {name:'小智4',age:33},
];
console.log(Array.from(arr, ({name}) => name));
// [ '小智1', '小智2', '小智3', '小智4' ]
console.log(arr.map(val => val.name));
// [ '小智1', '小智2', '小智3', '小智4' ]

将数组转换为对象

let arr = ['小智1', '小智2', '小智3', '小智4'];
let obj={...arr};
console.log(obj);
// { '0': '小智1', '1': '小智2', '2': '小智3', '3': '小智4' }

是否有这个属性

const hasKey = (obj, key) => {
  if (key.includes('.')) {
    let _key = key.split('.')[0];
    if (typeof obj[_key] === 'object')
      return hasKey(obj[_key], key.slice(key.indexOf('.') + 1))
  }
  return Object.keys(obj).includes(key);
}

let obj = {
  a: 1, b: { c: 4 }, 'd.e': 5
}
hasKey(obj, 'a'); // true
hasKey(obj, 'b'); // true
hasKey(obj, 'b.c'); // true
hasKey(obj, 'd.e'); // true
hasKey(obj, 'd'); // false
hasKey(obj, 'f'); // false

// 优化

const hasKey = (obj, keys) => {
  return (keys.length > 0) && keys.every(key => {
    //当没有这个属性
    if (typeof obj !== 'object' || !Reflect.ownKeys(obj,key)) {
      return false
    }
    obj = obj[key];
    return true
  })
};
let obj = {
  a: 1,
  b: { c: 4 },
  'b.d': 5,
};
console.log(hasKey(obj, ['b','c']));
console.log(hasKey(obj, ['b.d']));

对象转成网址的那种

const objectToQueryString = query => {
  if (query) {
    return Object.entries(query).reduce((acc, [key, val], index) => {
      const symbols = index === 0 ? '?' : '&';
      acc += typeof val === 'string' ? `${symbols}${key}=${val}` : '';
      return acc
    }, '')
  } else {
    return ''
  }
};
console.log(objectToQueryString({page: '1', size: '2ky', key: undefined}));
// ?page=1&size=2ky

判断偶数(从0开始)

const odd=num=>num%2===1;
console.log(odd(5));

获取当前时间

const currentTime = () => {
  let t = new Date();
  t.setHours(t.getHours() + 8);
  let arr = t.toISOString().split(/[T.]/);
  return arr[0]+' '+arr[1]
};

去重

let arr = [
  {age: 1, name: '张三'},
  {age: 1, name: '张三'},
  {age: 2, name: '李四'},
  {age: 3, name: '张三'},];
let arr1 = arr.map(val => val.name);
console.log(arr.filter((val, index) => arr1.indexOf(val.name) === index));
// [ { age: 1, name: '张三' }, { age: 2, name: '李四' } ]

判断两个数组的每一项是否相等

// a是小的,b是大的
const arrayEqual = (a, b) => {
  if (!(Array.isArray(a) && Array.isArray(b))) {
    return false
  }
  if (a.length !== b.length||a.length > b.length) {
    return false;
  }
  return a.reduce((acc, val, index) => val === b[index])
};
console.log(arrayEqual([1, 2, 3], [1, 2, 3])); //true
22|0Generator 函数遍历数组

Generator 函数遍历数组

let arr = [
  {name: 'zs',age: 38,gender: 'male'},
  {name: 'yw',age: 48,gender: 'male'},
  {name: 'lc',age: 28,gender: 'male'},
];
function* loop(arr) {
  for(let item of arr){
    yield item;
  }
}
let repoGen = loop(arr);
console.log(repoGen.next());
// { value: { name: 'zs', age: 38, gender: 'male' }, done: false }
console.log(repoGen.next());
// { value: { name: 'yw', age: 48, gender: 'male' }, done: false }

数组去重

function arr1(){
    var n=[];
    for(var i=0;i<arr.length;i++){
      if(n.indexOf(arr[i])==-1){
          n.push(arr[i])
      }
    }
    return n;
  }

再次提一些异步

const getUser = () => new Promise((resolve, reject) => {
  resolve('zhangsan');
  reject('失败')
}).then(resolver=>{
  console.log(resolver)
})

async function add() {
  console.log(1)
  await getUser()
  console.log(3)
}
add()
/*
* 1
zhangsan
3
* */

彻底弄懂怎么正确使用async/await

//微任务
const p1 = () => new Promise((resolve, reject) => {
    resolve('微任务')
}).then(res => {
    console.log(res)
})
//宏任务
const p2 = () => new Promise(res => setTimeout(() => {
    res('宏任务')
},1000)).then(res => {
    console.log(res)
})
const add = async () => {
    console.log(1)
    await p2()
    await p1()
    console.log(4)
}
add()

简化成函数
const pipeAsync = (...args) => arg => args.reduce((acc, val) => {
    return acc.then(val)
}, Promise.resolve(arg))

const sum = pipeAsync(
    x => x + 1,
    x => new Promise(resolve => setTimeout(() => {
        resolve(x * 4)
    }, 1000)),
    x => new Promise(res => res(x * 10)),
    x=>x+10

);
(
    async () => {
        //5+1   *4  *10  +10
        console.log(await sum(5))
    }
)()
const arrayFromRange = function arrayFromRange(min, max) {
    const output = []
    for (let i = min; i <= max; i++)
        output.push(i)
    return output
}
console.log(arrayFromRange(1, 10))
//[ 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 ]
//优化后
const arrayFrom = (min, max) =>
    Array.from({length: max - min+1}, (_, i) => i + min)
console.log(arrayFrom(1, 10))
//[ 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 ]