Adding javascript file to custom plugin?

Hi im trying to make a custom plugin and I need to create a client side action but in order for what im trying to do with that action to work I need to access a javascript file. I went to the shared section and included the file in a script tag but when I go to create an action and use a function from that script its not working is there anyway to do this thanks!

If you add the code you used to include the script, the code you are using in the plugin and the error (if any) that you get on execution you have better chances to receive help.