canvas. Unexpected ends of the line

I need to get a picture like this:

context.beginPath();
context.moveTo(20, 20);
context.lineTo(120, 70);
context.lineTo(220, 20);
context.lineWidth = 15;
context.stroke();
context.fillStyle = 'aqua';
context.fill();

But as a result, I get this picture:

Is it possible to get rid of such unexpected ends of the line?

>Solution :

In this particular case, you can just clear the rectangle above the triangle, as shown below.

The issue in general is that you’re drawing a 15-unit-wide line centered along the triangle’s edge; you’d have to compute how much to extend the line outside the triangle and halve its width, or to compute a similar filled polygon, to make this work in the general case.

var canvas = document.getElementById("c");
var context = canvas.getContext("2d");
context.beginPath();
context.moveTo(20, 20);
context.lineTo(120, 70);
context.lineTo(220, 20);
context.lineWidth = 15;
context.stroke();
context.fillStyle = 'aqua';
context.fill();
context.clearRect(10, 10, 210, 10);

<canvas id="c" width="240" height="100">