Array-Filter-Polyfill.js

if(!Array.prototype.filter){
  Array.prototype.filter = (fn) => {
    let res = []
    let length = this.length
    for(let i=0; i < length; i++) {
      if(fn(this[i])) {
        res.push(this[i])
      }
    }
    return res;
  }
}