The knowledge contained in this issue is prerequisite for another [issue](How to know where the library js file is loaded from local repository)

1). switch on development model by modifying web.xml file as below:

2). Suppose you would like to know where is this js file loaded from your local laptop:

you can find the answer here(Header name: x-sap-ResourceUrl):

Using this approach, if you would like to make changes on a given UI5 framework library file on your local laptop, you can first identify its file path in a certain jar file, and then perform the local change according to this guide.