数组去重

1.set

let unique = [...new Set([1,2,3,3,4,5,6,5])]

2.splice

let len = arr.length

for(let i = 0;i < len;i++) {
  for(let j = i + 1;j < len;j++) {
    if(arr[i] === arr[j]) {
      arr.splice(j,1)
      j--
      len--
    }
  }
}
console.log(arr)

• j和len都要减一是因为当splice去掉一个元素时，数组的长度会减一，所以j和len都应该减一

3.indexOf

let res = []
for(let i = 0;i < len;i++) {
  if(res.indexOf(arr[i]) === -1) res.push(arr[i])
}
console.log(res)

4.includes

for(let i = 0;i < len;i++) {
  if(!res.includes(arr[i])) res.push(arr[i])
}
console.log(res)

5.filter

let res = arr.filter((item,index) => {
  return arr.indexOf(item) == index
})
console.log(res)

6.map&set

let map = new Map()
let res = []
for(let i = 0;i < arr.length;i++) {
  if(!map.has(arr[i])) {
    map.set(arr[i],true)
    res.push(arr[i])
  }
}
console.log(res)