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;
}

• lexicore: Probably var et = this.eventType; is missing?
• Guffa: @lexicore: Yes, you are right. However, I rewrote the code so that it returns the same element as the original code.
• lexicore: Cool. I just added brackets around (et === Jsonix.XML.Input.START_ELEMENT).
• Guffa: @lexicore: That's not needed as the comparison has the highest precedence here, but you might want it for readability.
• lexicore: Correct, this was only for readability purposes.