How to set the value of an input field in JavaScript?

Hi, I'm trying to replicate an old survey of my Professor from a different software into Qualtrics. The one thing I'm struggling with is to add a button that people can click, and if they do, a (predetermined) value should show in a text box next to it... I have found some (javascript) code online that should be able to do exactly this (see link), however, it doesn't work in Qualtrics Javascript... Somehow, in Qualtrics, you can use <>? https://www.geeksforgeeks.org/set-the-value-of-an-input-field-in-javascript/ Does anyone know how to solve this? Thanks!