why the runtime error? how to define function context?

Question

https://code.sololearn.com/Wmi18XlUUZK9/?ref=app

Answer 1

// Fix your coding errors

var canvas = document.getElementById("canvas");
var context = canvas.getContext("2d");

window.onload = () => {
context.moveTo(0,0);
context.lineTo(600,400);
context.stroke();
}