SOURCE

let canvas = document.getElementById("canvas");
canvas.width=300;
canvas.height=300;
let context = canvas.getContext("2d");

context.beginPath()
context.moveTo(0,100);
context.lineTo(100,200);
context.lineTo(0,300);
context.lineWidth = 5;
context.strokeStyle = "red";
context.stroke()

context.beginPath()
context.moveTo(100,100);
context.lineTo(200,200);
context.lineTo(100,300);
context.lineWidth = 5;
context.strokeStyle = "blue";
context.stroke()

context.beginPath()
context.moveTo(200,100);
context.lineTo(300,200);
context.lineTo(200,300);
context.lineWidth = 5;
context.strokeStyle = "yellow";
context.stroke()

<canvas id="canvas"></canvas>