StringUtil.as

package com.utils
{
  public class StringUtil {
    static public function padStart(string:String, length:uint, padString:String = ' '):String {
      var insert:String = '';

      for (var i:int = 0; i < length; i++) {
        insert += padString;
      }

      return insert + string;
    }
  }
}

trace(StringUtil.padStart('Hello world!', 5, '.'));
// > ".....Hello World!"