Question

I tested the following code in IE6, IE7 and IE8 with the same result:

<a name="cd"/>a</a>
<script>
try {
cd = new Date;
} catch(e) {
alert(e);
}
</script>

In all cases an error is thrown. However using

var cd = new Date;

seems to solve the problem.
Does anyone know why that is ?

Here is an example: http://jsbin.com/ahuhu4/2

Answer 1

When you don’t use the var specifier to declare your variable, the variable cd is added as a property to the window object, e.g. window.cd. You already have an object element that is a child of window that is <a name="cd">a</a> which is already typed. You can’t specify new Date as a type for this object as it already exists. When you use the var keyword, you are rescoping the variable to a local scope and removing its direct attachment to the window object. This removes the error and allows IE to proceed. Other browser engines handle this differently.