es5,6,7,8常用总结

数组去重

• set去重

let arr = [1,2,3,4,3,5,4];
let set = new Set(arr);
let newArr = Array.from(set) //  Array.from会将类数组或者可遍历对象转为数组
console.log(newArr); //输出结果：1,2,3,4,5

• reduce去重
  对象数组中根据某个属性判断是否相同，存在相同的则删除。

let arr = [
  {id: 1, a: 10},
  {id: 2, a: 11, b: 5},
  {id: 1, c: 100},
  {id: 3, a: 10},
  {id: 2, a: 11, b:90}
]
let obj = {};
let newArr = arr.reduce(function(item, next) {
  obj[next.id] ? '' : obj[next.id] = true && item.push(next);
  return item;
}, []);
console.log(newArr) 
// 输出结果:[{id: 1, a: 10, {id: 2, a: 11, b: 5}, {id: 3, a: 10}]

• map去重

let arr = [ 1, 1, 2, 2, 3, 4, 4, 5, 9, 10, 5 ]
let newArr = []
let map = new Map()
arr.forEach(item => {
  map.has(item) ? map.set(item, true) : map.set(item, false)&&newArr.push(item)
});
console.log(newArr) // 输出结果：[1, 2, 3, 4, 5, 9, 10]

• map获取重复

let arr = [ 1, 1, 2, 2, 3, 4, 4, 5, 9, 10, 5 ]
let map = new Map()
arr.forEach(item => {
  map.set(item, map.has(item))
});
map.forEach((item, index) => {
  item === true ? console.log(index) : null
})
// 输出结果：1，2，4，5

• map获取第一位非重复

let arr = [ 1, 1, 2, 2, 3, 4, 4, 5, 9, 10, 5 ]
function findFirstNoRepeat(arr) {
  let map = new Map()
  arr.forEach(item => {
    map.set(item, map.has(item))
  });
  for (let [item, index] of map) {
    if (index === false) {
      return item
    }
  }
  return 'all repeat'
}
findFirstNoRepeat(arr)// return结果： 3

根据选中结果生成布尔数组

let arr = ["A", "B", "C", "D", "E"]
let selectedArr = ["C", "D"]
let boolArr = arr.map(item=>selectedArr.includes(item));
console.log(boolArr) // 返回结果[false, false, true, true, false]

字符串填充

• 字符串前填充

let bankCardNo = '1234567890123456'
let showLast4BankCardNo = bankCardNo.substr(-4).padStart(16,'*')
console.log(showLast4BankCardNo) // 输入结果：············3456

• 字符串后填充

let bankCardNo = '1234567890123456'
let showFront4BankCardNo = bankCardNo.substr(0, 4).padEnd(16,'·')
console.log(showFront4BankCardNo) // 输入结果：1234············

-字符串替换

let bankCardNo = '1234567890123456'
let showFront4BankCardNo = bankCardNo.replace(/(\d{4})\d+(\d{4})$/, "$1 ···· ···· $2")
console.log(showFront4BankCardNo) // 输入结果：1234 ···· ···· 3456

every和some

var ages = [3, 18, 20, 75, 0];
function someTest(age) {
  return age.some((item)=>{
    return item >= 18;
  })
}
function everyTest(age) {
  return age.every((item)=>{
    return item >= 18;
  })
}
console.log(someTest(ages)) // true
console.log(everyTest(ages)) // false

some是任一项为true，则为true
every是每一项为true，才为true
（持续补充ing...）