PRB: Placement of <Script> Tag Results in Unexpected Behavior

MORE INFORMATION

As an HTML page containing VBScript or JavaScript, code is loaded by Internet Explorer 3.0, it is parsed and compiled. If a form element makes a call to some function that is later defined within a <script> tag, errors can result if the form element does not use the proper calling conventions.

Internet Explorer 3.0 defaults to using the JavaScript compiler. When the compiler sees the form element, it generates JavaScript code to make the function call associated to the form element. If the <script> tag is defined after the form element and specifies Language="VBScript," this function call is syntactically incorrect and an error results.

To avoid this error, all <script> tags should be defined before any form or other objects that make functions calls. The preferred placement of the <script> tag is within the <Head></Head> tags. By using this placement, any function that may be called by a forms element has already been loaded and compiled.

Steps to Reproduce Behavior

The following HTML code demonstrates the problem:

<HTML>
<Head><title>a test</title></Head>
<body>

<form name="vbtest">
<input type="button" Name="Button1" value="Press Me"
onclick="btnPress">
</form>

<Script language="VBScript">
sub btnPress
    alert "you pressed the button"
end sub
</script>
</body>
</HTML>
				

Because the compiler reads the form definition first, it compiles the onClick event into a JavaScript reference. When the button is clicked, the interpreter tries to find the appropriate JavaScript function to execute. However, the function is in a block of VBScript code and is not seen by the interpreter as executable JavaScript code. Therefore, an "object doesn't support the property or method" error results.