IOS Safari, what is the first release of IOS to allow HTML/JAVASCRIPT files to be executed

I have a local HTML file containing javascript, which I have never been able to execute with IOS, by double-clicking the file. This has always worked on Android.
I recently had access to a new iPad and the file was in Dropbox. I opened Dropbox, double clicked the filename and it worked perfectly. It contains quite a large database formatted as JSON.
Can anyone advise me as to what was the earliest version of IOS to allow this behaviour as I know several people with iPhones and iPads, who would like to use this database.