Question

So I was programming some stuff in Javascript and some time later I saw I made a typo in the following piece of code:

(function() {

    var someEl = document.getElementById('id-of-some-el'),l    <-----
        someOtherEl = document.getElementById('some-other-el');

    someEl.onclick = function() {
       ...
    };

})();

Notice how the l isn’t supposed to be there. I’ve only tested this in Firefox but, why didn’t I get a syntax error?

Answer 1

You were trying to create two variables inside the var-statement:

var someEl = document.getElementById('id-of-some-el'),
    someOtherEl = document.getElementById('some-other-el');

The introduction of the comma meant that you created someEl and l:

var someEl = document.getElementById('id-of-some-el'),l

Semicolons at the end of JS lines are optional, so now you have a distinct, second line of code afterwards:

    someOtherEl = document.getElementById('some-other-el');

And this is valid because you can assign to variables without explicitly var-ing them (albeit imbuing slightly different semantics to your program).