this is what i came up with:

Array.prototype.myFilter = function(callback) {
const finalArray = []

for(let i = 0; i<this.length; i++) {
  const res = callback(this[i],i,this)
  if(res) finalArray.push(this[i])
  }

  return finalArray
}

const res = [1,2,3,4,5,6].myFilter((val) => val % 2 === 0)