基础类型数组去重

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const arr = [1, 1, 2, 3, 3, 4, 5]

ES5

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function unique(arr) {
  return arr.filter((item, index, array) => array.indexOf(item) === index)
}

ES6

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function unique (arr) {
  const seen = new Map()
  return arr.filter((a) => !seen.has(a) && seen.set(a, 1))
}
// or
function unique(array) {
    return [...new Set(array)]
}

复杂类型数组去重

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const array = [{value: 1}, {value: 1}, {value: 2}]

ES5

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function unique(arr) {
    var obj = {}
    return arr.filter((item, index, array) => !obj.hasOwnProperty(JSON.stringify(item)) && (obj[JSON.stringify(item)] = true))
}

ES6

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function unique (arr) {
  const seen = new Map()
  return arr.filter((a) => !seen.has(JSON.stringify(a)) && seen.set(JSON.stringify(a), 1))
}