Can someone please help me with this Javascript calculator?

Question

So I already created this calculator using document.write() but since it's bad practice I wanted to create one by making a paragraph and using innerHTML() to insert the calculations into the paragraph. Can someone please help me with this? Here is my code:
https://code.sololearn.com/WjqXp2xoGAIS

Answer 1

document.getElementById('p').innerHTML= mystr;

Add js code between

window.onload = () =>{
//js here
}
better add functions out side this.