filterArray

function filterList(array) {
    let j = 0;
    let numbers = [];

    for (let i = 0; i < array.length; i++) {
        if (typeof (array[i]) == 'number') {
            numbers[j] = array[i];
            j++;
        }
    }

    return numbers;
}

let dirtyArray = [1, 2, 'a', 'b'];
console.log(' array1:   ' + "[" + filterList(dirtyArray) + "]");

let numbers = filterList([1, 'a', 'b', 0, 15]);
console.log(' array2:   ' + "[" + numbers + "]");

dirtyArray = [1, 2, 'aasf', '1', '123', 123];
numbers = filterList(dirtyArray);
console.log(' array3:   ' + "[" + numbers + "]");