Simon is programming a Logo code editor, but is stuck with one tricky function

Simon is programming a full implementation Logo code editor in p5.js (JavaScript), as part of Coding Train’s Logo Coding Challenge. Logo is a coding language that Simon says he has been learning via Turtle Academy, a site containing 20 lessons. He has already created most of the editor (got as far as lesson 17 on Turtle Academy) but got stuck with the fill function in Logo (he doesn’t know how to program the fill function). Can anyone help him out? Simon’s code is online at: https://editor.p5js.org/simontiger/sketches/BknVvCFTm