removing elements from array which are not numbers using pure js

I'm stuck with one task, hope you could help me

I have to return an combined array which consist only from numbers. So if the element has got except for number another character, such element should be removed.

I had few ideas. Unfortunately, none of them work properly. providing my code

function combineArray(arr1, arr2) {
    let array1 = filt(arr1);
    let array2 = filt(arr2);
    let arr3 = array1.concat(array2);
    return arr3;
}
function filt(array){
  array.forEach(function(item,index) {
    if (typeof item !== 'number'){
      array.splice(index, 1);
  }
  })
  return array;
}

Here's a simple solution that uses the filter method on arrays and Number.isFinite to check if a variable is a number:

function combineArray(arr1, arr2) {
    let array1 = filt(arr1);
    let array2 = filt(arr2);
    let arr3 = array1.concat(array2);
    return arr3;
}

function filt(array) {
  return array.filter(x => Number.isFinite(x));
}


console.log(combineArray(['item1', 2, 3, 'item4'],['1','second','3rd',4]));

This outputs: [2, 3, 4]