Subtle error in JavaScript tutorial

[Guest ZeroG]

I just noticed a slight error in the JavaScript tutorial in the JS Variables section:

Assigning Values to Undeclared JavaScript VariablesIf you assign values to variables that has not yet been declared, the variables will automatically be declared.These statements:

x=5;carname="Volvo";

have the same effect as:

var x=5;var carname="Volvo";

I discovered after quite a bit of work that it's not quite that simple. Actually, JavaScript will declare variables as globals if you don't use the var statement - otherwise, it observes scope rules basically the same way C does. As an example, consider the following code:

	function outer() {		for (i = 0; i < 5; i++) {			document.write("outer: " + i + "<br />");			inner();		}	}		function inner() {		for (i = 0; i < 3; i++) {			document.write("inner: " + i + "<br />");		}	}		outer();

If you execute this (I tried in IE 7 and FF 2), you will get an infinite loop and your browser will ask you to stop the script. The output is:

outer: 0inner: 0inner: 1inner: 2outer: 4inner: 0inner: 1inner: 2outer: 4inner: 0inner: 1inner: 2outer: 4...

As you can see, the i in outer keeps getting set to 3 after inner exits, and then it gets incremented to 4 every time. However, if you use var i = 0 instead of just i = 0, it works as expected. Just a suggestion - you might want to put some kind of note in the variable section that not using var makes JavaScript declare variables as global. I didn't know that until last week, and it might be good for folks just starting out to know that.