Adam de Boor revealed how many lines of code are in Gmail: 443,000 lines of JavaScript code written by hand.

Gmail’s recent update brought us a strange new UI element:1



Clicking on the checkbox selects all emails. The arrow, on the other hand, allows you to make more specific selections:

Currently, the Gmail program is comprised of 443,000 lines of JavaScript, with 978,000 lines if comments are included. All of it was written by hand, he said.