I could not find any function like "clearRect" on p5js. Maybe I have to use "erase" function in p5js. But you can use "clearRect" with context2D easily.
with context2D
let ctx:CanvasRenderingContext2D = this._p5.drawingContext; ctx.clearRect(xx,yy,ww,hh);
Erase function on p5js
this._p5.erase(); this._p5.fill(0); this._p5.noStroke(); this._p5.rect( xx,yy,ww,hh ); this._p5.noErase();