1. If you want to pass a value generated by ColdFusion to JavaScript, ColdFusion needs to output the value to the page whereupon JavaScript can be used to read the value. Typically you may put the value into a formfield, give the field an ID, which can then be referenced by JavaScript.

2. If you want to use a value generated by JavaScript, you could write it into a form field and submit the form. ColdFusion can then process the submitted data.

Alternatively, JavaScript can make an AJAX request to a ColdFusion webservice, passing JavaScript generated values and or values read from the web-page using JavaScript.

3. … I won’t mention the third way as it’s a nasty hack and should be avoided at all costs. Needless to say it relates to dynamically rendering the JavaScript with ColdFusion.