Question

just for my knowledge –

what happens if i have 2 equals JS files in my document :

    <script src='A.js'>
and
    <script src='B.js'>

A.js and B.js are equal content .

what happens if i run one func for example which resides in both files ?

which function will fire ? does in memory it has 2 functions ?

what about this situation :

    <script src='A.js'>
and
    <script src='A.js'>

does it even load it again ?

i need some clarification..

Answer 1

case (1):
<script src='A.js'>
and
<script src='B.js'>
have the same content:

The file B.js is loaded later, and overrides whatever was defined in A.js. Each function and variable is defined only once, and its value is whatever was assigned to it the last.

case (2):
<script src='A.js'>
<script src='A.js'>
Here, your browser uses caching, for it has no reason to load a file which contents are already known to it. The same is done for images (picture files).
Even if you will refresh the page, chances are, the file A.js will not be loaded again, but the cached version will be used (that’s if you press F5, Ctrl+F5 will force the browser to reload everything)