js数组去重

filter()去重

  [1,2,3,4,3,2,1].filter((item,index,arr)=>arr.indexOf(item)===index)

new Set()去重

  let arr = [...new Set([1,2,3,4,3,2,1])]

reduce()去重

  let arr = [1,2,3,4,3,2,1].reduce((x, y) => {
      return x.includes(y) ? x: x.concat(y);
  }, []);