code: function repeat(str, n) {
      n = n ? Number(n) : 0;
      if(n != n){ // NAN
          n = 0;
      }
  
      n = Math.floor(n);
  
      if(n <= -1){
          n = 0;
      }
      
      str = '' + str;
  
      var ret = '';
      while(n !== 0){
          if(n & 1 === 1){
              ret += str;
          }
          str += str;
          n >>>= 1;
      }
      return ret;
  }
docs: @description return a string which build by repeat the given str n times.
  
  {{ 'abc' | repeat 3 }} => 'abcabcabc'