Highlight Duplicates Above in Google Sheets with Apps Script

https://github.com/lsvekis/Apps-Script-Code-Snippets Duplicates in a spreadsheet aren’t always “bad”—but sometimes they’re a sign of a problem. A common pattern is: you want values to be unique as you enter them, and if someone repeats a value that already appeared earlier in the same column, you want an instant visual warning. In this tutorial, you’ll build an ...