flatten array

flatten.js

function flatten(arr, result) {
    result = result || []

    arr.forEach(function(item) {
        if (Array.isArray(item)) {
            flatten(item, result)
        } else {
            result.push(item)
        }
    })
    return result
}

// test
console.log(flatten([
    [3],
    [[5], [[[9]]]]
]))