class SomeClass{
    constructor(){}
    mainMethod(HTMLElement|PaperElement element, StreamBuffer stream) /* I select this */
}

class SomeClass{
    constructor(){}
    mainMethod(element, stream){
        if(element instanceof HTMLElement || element instanceof PaperElement){
            if(stream instanceof StreamBuffer){
               /* My cursor appear here */
            }
            else{
                throw new TypeError('2nd argument should be StreamBuffer');
            }
        }
        else{
          throw new TypeError('1st argument should be HTMLElement or PaperElement');
        }
    }
}

class SomeClass{
      ...
      otherMethod(String str, notypearg, [optionalarg]) /* I select this */
  }

class SomeClass{
      ...
      otherMethod(str, notypearg, optionalarg){
          if(typeof(str) == 'string'){
              if(notypearg){
                  /* My cursor appear here */
                  // nothing for optionalarg
              }
              // No error for args without type
          }
          else{
              throw new TypeError('1st argument should be String');
          }
      }
  }