数组去重

1. Array.filter() + indexOf

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

2. 双重 for 循环

function distinct(arr) {
	let len = arr.length
    for (let i = 0; i < len; i++) {
        for (let j=i+1; j<len; j++) {
            if (arr[i] == arr[j]) {
                arr.splice(j, 1);
                // splice 会改变数组长度，所以要将数组长度 len 和下标 j 减一
                len--;
                j--;
            }
        }
    }
    return arr
}

3. for…of + includes()

function distinct(arr) {
    let result = []
    for (let i of arr) {
        !result.includes(i) && result.push(i)
    }
    return result
}

4. Array.sort() + for

function distinct(arr) {
    arr = arr.sort()
    let result = [arr[0]]

    for (let i=1, len=arr.length; i<len; i++) {
        arr[i] !== arr[i-1] && result.push(arr[i])
    }
    return result
}

5. new Set()

function distinct(arr) {
    return Array.from(new Set(arr))
	return [...new Set(arr)]
}

6. for…of + Object

function distinct(arr) {

    let result = []
    let obj = {}

    for (let i of arr) {
        if (!obj[i]) {
            result.push(i)
            obj[i] = 1
        }
    }

    return result
}