In SharePoint 2013 we are able to see the option “overwrite Existing files” while attaching documents in Document library. By default the option will be checked most of time by mistakenly end users will upload document with same name so that they can miss the existing document.
To avoid that we will Uncheck that option, so that if they are trying to upload the same name document it will throw error.
We implemented this functionality using JQuery and added in the master page, this will effect only in that particular site only.
Step 1: Download the master and rename it.
In the new master page we added the JQuery JS file and script as shown below screen shot.We already uploaded the JS file in the same site in Site Assets library.
Step 2: Upload the new master page and select the master page for that particular site alone.