Flattern array self implementations

with-reduce-finite.js

let depthTraversed = 1;

function flattenArray(arr, depth) {
    return arr.reduce((acc, current) => {
        if (Array.isArray(current)) {
            if (depthTraversed > depth) {
                acc = acc.concat([current]);
                return acc;
            }
            depthTraversed++;
            acc = acc.concat(flattenArray(current, depth));
            depthTraversed--;
        } else {
            acc = acc.concat([current]);
        }
        return acc;
    }, []);
}

const result = flattenArray([1, 2, [3], [[4]], [5, 6], [[[7]]], [[[[[10]]]]], 2], 2);
console.log(JSON.stringify(result));

with-reduce-infinite.js

function flattenArray(arr){
    return arr.reduce((acc, current, index) => {
        if(Array.isArray(current)){
           acc = acc.concat(flattenArray(current));
        } else {
          acc = acc.concat([current]);
        }
        return acc;
    }, []);
}

flattenArray([1, 2, [3], [[4]], [5,6], [[[7]]]]);// [1,2,3,4,5,6,7]

without-reduce-finite.js

let depthTraversed = 1;
function flattenArray(arr, depth) {
    let flattenedArray = []
    if (!Array.isArray(arr)) {
        return arr;
    }
    for (let i = 0; i < arr.length; i++) {
        if (Array.isArray(arr[i])) {
            if (depthTraversed > depth) {
                flattenedArray = flattenedArray.concat([arr[i]]);
            } else {
                depthTraversed++;
                flattenedArray = flattenedArray.concat(flattenArray(arr[i], depth));
                depthTraversed--;
            }
            continue;
        }
        flattenedArray.push(arr[i]);
    }
    return flattenedArray;
}

const result = flattenArray([1, 2, [3], [[4]], [5, 6], [[[7]]], [[[[[10]]]]], 2], 2);
console.log(JSON.stringify(result));

without-reduce-infinite.js

function flattenArray(arr) {
    let flattenedArray = []
    if (!Array.isArray(arr)) {
        return arr;
    }
    for (let i = 0; i < arr.length; i++) {
        if (Array.isArray(arr[i])) {
            flattenedArray = flattenedArray.concat(flattenArray(arr[i]));
            continue;
        }
        flattenedArray.push(arr[i]);
    }
    return flattenedArray;
}

const result = flattenArray([1, 2, [3], [[4]], [5, 6], [[[7]]], [[[[[10]]]]], 2]);
console.log(result);