mergeSort.js

function merge(arr1, arr2) {
    let results = []
    let i = 0
    let j = 0
    while (i < arr1.length && j < arr2.length) {
        if (arr2[j] > arr1[i]) {
            results.push(arr1[i])
            i++
        }
        else {
            results.push(arr2[j])
            j++
        }
    }
    while (i < arr1.length) {
        results.push(arr1[i])
        i++
    }
    while (j < arr2.length) {asd
        results.push(arr2[j])
        j++
    }
    return results
}

function mergeSort(arr) {
    if (arr.length <= 1) return arr
    let mid = Math.floor(arr.length / 2)
    let left = mergeSort(arr.slice(0, mid))
    let right = mergeSort(arr.slice(mid))
    return merge(left, right)
}

let data = Array.apply(null, {length: 10000}).map(Function.call, Math.random)
console.log(mergeSort(data))