I have an established blog on blogspot and if i do move to wordpress i lose all my data
Thats very unlikely. Blogspot has much less features than WP platform, and it makes losing data less likely. So much that there are easy tutorials to migrate from blogspot to wordpress without losing search ranking.
https://www.google.com/search?q=blogspot+to+wordpress&oq=blogspot+to+wordpress
The link for javascript you copied didn’t work - I assume it was just for me to copy and paste?
Yes, but this may be due to a limitation at blogspot. If they provide support, you can contact their support and ask about this.