数组获取重复、获取非重复

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保留数组中的非重复数据

let arr = [11, 23, 26, 23, 11, 9]
const filterNonUnique = arr => arr.filter(i => arr.indexOf(i) === arr.lastIndexOf(i))

console.log(filterNonUnique(arr));  // [ 26, 9 ]

保留数组中的重复数据

let arr = [11, 23, 26, 23, 11, 9]
const filterUnique = arr => arr.filter(i => arr.indexOf(i) !== arr.lastIndexOf(i))

console.log(filterUnique(arr)); // [ 11, 23, 23, 11 ]