Pluggin must be in same folder as html file?

Pluggin must be in same folder as html file?

Two downloaded html programs that run fine do not run properly when .js (jQuery pluggin file) is placed in a separate  js folder and not left in the same folder as the html program. As with most .js files they should be able to be referenced in the html file as: js/jQuerypluggin.js or whatever the proper name is.

The jQuery files (pluggins) will only run when in the same folder as the referencing html file.

Please explain why, since not every pluggin I have used does this.

Thanks,

davidre