去重

利用 ES6 Set 去重

function unique(arr) {
  return Array.from(new Set(arr))
}
let arr = [1, 2, 3, 4, 5, 1, 2, 3]
console.log(unique(arr))
// [1, 2, 3, 4, 5]

利用当前项和剩余项比较去重

方法较多，这里用比较典型的indexOf()方法

function unique(arr) {
  let newArr = []
  for (let i = 0; i < arr.length; i++) {
    let current = arr[i]
    let residue = arr.slice(i + 1)
    if (residue.indexOf(current) === -1) {
      newArr.push(current)
    }
  }
  return newArr
}
let arr = [1, 2, 3, 4, 5, 1, 2, 3]
console.log(unique(arr))
// [4, 5, 1, 2, 3]

先排序，再进行遍历及相邻元素比对去重

function unique(arr) {
  arr.sort((a, b) => a - b)
  let newArr = [arr[0]]
  for (let i = 1; i < arr.length; i++) {
    if (arr[i] !== arr[i - 1]) {
      newArr.push(arr[i])
    }
  }
  return newArr
}
let arr = [1, 2, 3, 4, 5, 1, 2, 3]
console.log(unique(arr))
// [4, 5, 1, 2, 3]

利用对象的属性不能相同的特点进行去重

function unique(arr) {
  let obj = {}
  let newArr = []
  for (let i = 0; i < arr.length; i++) {
    current = arr[i]
    if (!obj[current]) {
      obj[current] = 1
      newArr.push(current)
    }
  }
  return newArr
}
let arr = [1, 2, 3, 4, 5, 1, 2, 3]
console.log(unique(arr))
// [1, 2, 3, 4, 5]