Friday, January 14, 2011

JavaScript Implementation In Different Browsers

In Hebrew, when counting or describing objects, it matters whether the object is considered as male or female. A table is male, while a television is female. As far as I know, this rule applies to Russian and other languages as well.
What's nice about humans is that if they use the wrong form, like a female form for a table, people around them would still understand what they're talking about. Although some might think that the language is ruined. That's OK.

When it comes to programming languages, things are different. Computer languages are supposed to be considered as an exact science, thus, if one not using the syntax correctly, the code won't execute.

Or so we'd like to think.

Consider this loop in JavaScript:
var i = 0;
do {
} while(i<2);

As you might expect, it would popup an alert box with "done:2" as the message. This would work on any JavaScript implementation I'm aware of.
Now, let's make a tiny difference (like using the female form in Hebrew, which is only a bit different than the male form):
var i = 0;
do {
}; while(i<2);

What was changed? Notice the semicolon (;) before the "while" statement. Try this using your favorite browser. If you get "done:2" as before, I urge you to replace your favorite browser immediately.
This piece of code shouldn't work. It has a syntax error. The semicolon is "unexpected".

Internet Explorer ignores that, and the code works as before. Other browsers (Firefox, Chrome) would halt the script execution.

I'm willing to forgive when people don't follow the Hebrew syntax down to the last rule, but when it comes to code - I'm unforgiving. Moreover, I'm unforgiving to the guys that implemented a "fuzzy" interpreter for a programming languages. This is supposed to be an exact science.

Let me give you another example. In this case, I'm not sure with which implementation I agree:
alert([1, 2, 3, ].length);
alert([1, , 2, 3].length);

Firefox and Chrome would print "3" and then "4", while Internet Explorer would print "4" twice. Basically, each array has an "empty" (undefined) element, so their length is supposed to be the same. But it appears that Firefox and Chrome would drop that element if it is the last one in the array.


  1. The nice thing about programming languages that have specifications is that you don't need to "agree" with any implementation; you can just check the spec.

    (Page 63, "If an element is elided at the end of an array, that element does not contribute to the length of the Array.").

  2. Israel, that was also my point. This is how it should be. But it's not.

    The JScript 5.8 engine included with the IE browsers family is claimed to be ECMAScript-262 Edition 3 compliant. That's exactly the same edition the rest of the browsers' engine are compliant with. So it appears you can be granted the "compliant" status without following the specs, or simply stay behind with everyone regarding the Edition of the spec (the current is 5).

  3. Its really interesting to know about the javascript and its implementation in different browsers.Thanks for sharing it.
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