Implementation of QuickSort using ES6 features

quicksort.js

// Using comprehensions
function sort(arr) {
    var pivot, t;
    if (arr.length === 0) {
        return [];
    }
    [pivot, t] = [arr[0], arr.slice(1)];
    return sort([x for (x of t) if x < pivot])
        .concat(pivot)
        .concat(sort([x for (x of t) if x >= pivot]));
}

// Using arrows with filter
function sort(arr) {
    var pivot, t;
    if (arr.length === 0) {
        return [];
    }
    [pivot, t] = [arr[0], arr.slice(1)];
    return sort(t.filter(x => x < pivot))
        .concat(pivot)
        .concat(sort(t.filter(x => x >= pivot)));
}

// Erlang equivalent
sort([Pivot|T]) ->
    sort([ X || X <- T, X < Pivot]) ++
    [Pivot] ++
    sort([ X || X <- T, X >= Pivot]);
sort([]) -> [].

you don't really need concat neater.

function sort(arr) {
    if (!arr.length) {
        return [];
    }
    let pivot = arr.pop();
    return [
         ...sort([x for (x of arr) if x < pivot]),
         pivot,
         ...sort([x for (x of arr) if x >= pivot])
    ]
}