Javascript Array newunshift( arg )

Array.prototype.newunshift = function( arg ){
  
  if( arg != null && arg != undefined && arg != "" && arg != this[ 0 ] && arg != this[ 1 ] ){  
    //from   www . ja  v  a  2  s .c  o  m
    if( this.length > 0 ){
      
      this[ 1 ] = this[ 0 ];
    }
      
    if( this.length > 1 ){
      
      this.splice( 2, 1 );
    }
  
    this[ 0 ] = arg;
  }
};