How can I eliminate unused .js code from my website pages?

[Magic001]

Hi, 
we start working on our website and we mentioned, we have lots of unused .js code on our website.
I wonder, how can we remove that and keep that just the page which uses that. For example, we have an estimated delivery app whish show the estimated delivery information on the product page, but we have this js file on every page. Can we remove that and use them on the product page directly?