Finding the next XML element

Question

I am looking for a better way to do a while cycle with the variable update.

The background is that I'm writing a StAX-line XML reader in JavaScript and want to implement a skipElement function. The function may only be called on the start tag and should skip everything until the closing end tag.

• this.nextTag() skips to the next tag and returns Jsonix.XML.Input.START_ELEMENT or Jsonix.XML.Input.END_ELEMENT depending on whether it is a start or an end tag.
• numberOfOpenTags holds the number of open tags, increased/decreased accordingly.
• If we have a closing tag and numberOfOpenTags is 1, we're done.

skipElement : function() {
    if (this.eventType !== Jsonix.XML.Input.START_ELEMENT) {
        throw new Error("Parser must be on START_ELEMENT to skip element.");
    }
    // We have one open tag at the start
    var numberOfOpenTags = 1;
    // Skip to the next tag
    var et = this.nextTag();
    // If we have an END_ELEMENT and there is exactly one tag still open, we're done
    while (et !== Jsonix.XML.Input.END_ELEMENT || numberOfOpenTags !== 1)
    {
        if (et === Jsonix.XML.Input.START_ELEMENT)
        {
            numberOfOpenTags++;
        }
        else
        {
            numberOfOpenTags--;
        }
        et = this.nextTag();
    }
    return et;
}

I am looking for improvements. What I don't like:

• this.nextTag() is called on two occasions.
• Another check for et within the cycle: if (et === Jsonix.XML.Input.START_ELEMENT).
• Too verbose if/else in the cycle.

Answer 1

How about don't go to the next element before the loop, just check for the counter to reach zero, get the next element first in the loop, and the use a conditional operator to determine how to change the counter:

skipElement : function() {
  if (this.eventType !== Jsonix.XML.Input.START_ELEMENT) {
    throw new Error("Parser must be on START_ELEMENT to skip element.");
  }
  var numberOfOpenTags = 1;
  var et;
  while (numberOfOpenTags > 0) {
    et = this.nextTag();
    numberOfOpenTags += et === Jsonix.XML.Input.START_ELEMENT ? 1 : -1;
  }
  return et;
}