// 数组去重

let arr = ['a', 'b', 'b', 1, 1, 'true', true, true, NaN, NaN, 'NaN', undefined, undefined, null, null];

// 1. 集合

unique1 = arr => [...new Set(arr)];

// 2. 双循环

unique2 = arr => {

    let array = [];

    arr.forEach(item => {

        if (!array.includes(item)) {

            array.push(item);

        }

    })

    return array

}

// 3. 对象的属性 / Map的key 唯一性

unique3 = arr => {

    const map = new Map();

    return arr.filter(item => !map.has(item) && map.set(item, 1))

}

unique4 = arr => {

    let obj = {}

    return arr.filter(item => !obj[typeof item + item] && (obj[typeof item + item] = 1))

}

// 4. 排序

unique5 = arr => {

    arr = arr.sort()

    let res = [arr[0]]

    for (let i = 1; i < arr.length; i++) {

        if (arr[i] !== arr[i - 1]) {

            res.push(arr[i])

        }

    }

    return res

}