Add sortBy in Array object

sortby.js

(function(){
  if (typeof Object.defineProperty === 'function'){
    try{Object.defineProperty(Array.prototype,'sortBy',{value:sb}); }catch(e){}
  }
  if (!Array.prototype.sortBy) Array.prototype.sortBy = sb;

  function sb(f){
    for (let i=this.length;i;){
      let o = this[--i];
      this[i] = [].concat(f.call(o,o,i),o);
    }
    this.sort(function(a,b){
      for (let i=0,len=a.length;i<len;++i){
        if (a[i]!=b[i]) return a[i]<b[i]?-1:1;
      }
      return 0;
    });
    for (let i=this.length;i;){
      this[--i]=this[i][this[i].length-1];
    }
    return this;
  }
})();