Perspective camera FOV slider help!

so right now i have a slider on my html and it ranges from 1-200. ive tried to put the variable name of it (output) where the fov value should be but it just breaks. ive tried to have other things such as document.getelementbyid and the id is demo but i have no clue on how to get it to work. my first time here so be nice.

“… but it just breaks.” Be more specific.

See the source code of this Three.js example. (Click on the “<>” button in the lower-right corner of the screen to view the demo’s source code.