see: http://bytes.com/groups/javascript/89023-difference-between-return-true-return-false
When you return something from a function, that value gets returned to the
caller. For instance, say I had a method to multiply two numbers. Maybe the
code looks like this:
function multiply(num1, num2) {
return num1 * num2;
}
result = multiply(2, 4);
The function multiply will return the result of it’s multiplication to
wherever it was called. The right-hand side of the result assignment is
where the function is called, so that is where the result is returned to.
So, in this case (with the parameters 2 and 4), it is the same as writing
result = 8;
When you are using return true or false with markup, you are indicating
whether or not you want the default action to happen after the javascript
has been executed. An example is needed:
<a href="somepage.html" onClick="alert(‘Hi’); return true;">Click Me</a>
When the link is clicked the javascript code for the onClick will run first,
and we get an alert. We have used return true, so that is saying when we
click OK to remove the alert, we do want to run the markup. So in this case
once we click OK to dismiss the alert, we would then be taken to
somepage.html. If we changed that to return false we would get the alert,
but wouldn’t go to somepage.html.