07-29-2007

Strict JavaScript Notation in Safari

I just spent an embarrassing amount of time trying to fix a JavaScript class to work in Safari. The class has worked from the outset in Firefox, but when I tried it in Safari, I got nothing. I’m using Safari 2.0.4, and by default, Safari will silently ignore JavaScript errors, making it really hard to debug a failing JavaScript. Taken from the Safari Developer FAQ, type the following command line instruction to enable the Debug menu in Safari:

defaults write com.apple.Safari IncludeDebugMenu 1

Once debugging was enabled, I could see that I had a syntax error on the last line of my class. This usually means a missed parentheses, unclosed bracket or something of the sort. I scoured my class from top to bottom, and couldn’t find a syntax error. I was even more confounded because the class wasn’t generating any errors whatsoever in Firefox. And finally I figured it out: one errant comma following the last method in my class, as follows:

Boxes = Class.create();
 
Boxes.prototype = {
 
  .
  .
  .
 
  getRow: function(box) {
    offset = Position.cumulativeOffset(box)[1] - this.bodyPadding;
    row = Math.floor(offset / this.boxHeight);
    return row + this.randomRow + 1;
  },
 
};

To Safari, the comma indicated that another method was to follow the getRow function, and when none was found, it generated a syntax error. It’s interesting that the same code in Firefox didn’t cause such an error, but with the comma removed, it works in both browsers.