Array Question

onlynumbers.js

let array = [1, 2, 3, '4', undefined, 'a', [], null];

function onlyNumbers(arr) {
    //  We create an array to output
    let output = [];
    //  We use forEach() to check if the type of every element is the string 'number'
    //  because we know that it outputs a lowercase string with the type.
    //  If true, we push the element to the output.
    arr.forEach(e => { if (typeof (e) === 'number') { output.push(e) } })
    return output
}

console.log(onlyNumbers(array));

//  Wich outputs [ 1 , 2 , 3 ]