function Point(x,y){this.x = x, this.y = y}
var strokeWidth = 20;
var V1 = new Point(-100,50);
var V2 = new Point(100,50);
var V3 = new Point(0, -100);
var ctx = triangle.getContext("2d"), ctxRect = ctx.canvas.getBoundingClientRect();
function drawPoints () {
ctx.clearRect(0,0,ctxRect.width,ctxRect.height);
ctx.strokeStyle = ctx.fillStyle = "#fa0";
ctx.fillRect(V1.x+ctxRect.width / 2,V1.y+ctxRect.height / 2,5,5);
ctx.fillRect(V2.x+ctxRect.width / 2,V2.y+ctxRect.height / 2,5,5);
ctx.fillRect(V3.x+ctxRect.width / 2,V3.y+ctxRect.height / 2,5,5);
ctx.beginPath();
ctx.moveTo(V1.x+ctxRect.width / 2+2,V1.y+ctxRect.height / 2+2);
ctx.lineTo(V2.x+ctxRect.width / 2+2,V2.y+ctxRect.height / 2+2);
ctx.lineTo(V3.x+ctxRect.width / 2+2,V3.y+ctxRect.height / 2+2);
ctx.lineTo(V1.x+ctxRect.width / 2+2,V1.y+ctxRect.height / 2+2);
ctx.closePath();
ctx.stroke();
var len = Math.sqrt(V1.x*V1.x+V1.y*V1.y);
var dx = V1.x / len, dy = V1.y / len;
var V1outer = new Point(V1.x + dx * strokeWidth, V1.y + dy * strokeWidth);
var V1inner = new Point(V1.x - dx * strokeWidth, V1.y - dy * strokeWidth);
console.log(V1outer);
len = Math.sqrt(V2.x*V2.x+V2.y*V2.y);
dx = V2.x / len, dy = V2.y / len;
var V2outer = new Point(V2.x + dx * strokeWidth, V2.y + dy * strokeWidth);
var V2inner = new Point(V2.x - dx * strokeWidth, V2.y - dy * strokeWidth);
len = Math.sqrt(V3.x*V3.x+V3.y*V3.y);
dx = V3.x / len, dy = V3.y / len;
var V3outer = new Point(V3.x + dx * strokeWidth, V3.y + dy * strokeWidth);
var V3inner = new Point(V3.x - dx * strokeWidth, V3.y - dy * strokeWidth);
ctx.strokeStyle = ctx.fillStyle = "#F00";
ctx.fillRect(V1outer.x+ctxRect.width / 2, V1outer.y+ctxRect.height / 2, 5,5);
ctx.fillRect(V2outer.x+ctxRect.width / 2, V2outer.y+ctxRect.height / 2, 5,5);
ctx.fillRect(V3outer.x+ctxRect.width / 2, V3outer.y+ctxRect.height / 2, 5,5);
ctx.beginPath();
ctx.moveTo(V1outer.x+ctxRect.width / 2+2,V1outer.y+ctxRect.height / 2+2);
ctx.lineTo(V2outer.x+ctxRect.width / 2+2,V2outer.y+ctxRect.height / 2+2);
ctx.lineTo(V3outer.x+ctxRect.width / 2+2,V3outer.y+ctxRect.height / 2+2);
ctx.lineTo(V1outer.x+ctxRect.width / 2+2,V1outer.y+ctxRect.height / 2+2);
ctx.closePath();
ctx.stroke();
ctx.strokeStyle = ctx.fillStyle = "#0F0";
ctx.fillRect(V1inner.x+ctxRect.width / 2, V1inner.y+ctxRect.height / 2, 5,5);
ctx.fillRect(V2inner.x+ctxRect.width / 2, V2inner.y+ctxRect.height / 2, 5,5);
ctx.fillRect(V3inner.x+ctxRect.width / 2, V3inner.y+ctxRect.height / 2, 5,5);
ctx.beginPath();
ctx.moveTo(V1inner.x+ctxRect.width / 2+2,V1inner.y+ctxRect.height / 2+2);
ctx.lineTo(V2inner.x+ctxRect.width / 2+2,V2inner.y+ctxRect.height / 2+2);
ctx.lineTo(V3inner.x+ctxRect.width / 2+2,V3inner.y+ctxRect.height / 2+2);
ctx.lineTo(V1inner.x+ctxRect.width / 2+2,V1inner.y+ctxRect.height / 2+2);
ctx.closePath();
ctx.stroke();
}
drawPoints();
strokeInput.oninput = function () {strokeWidth = this.value; drawPoints()}
#triangle { border: 1px dashed black; }
<label>Stroke Width: <input id="strokeInput" type="range" min="0" max="50" value="20"/></label><br/>
<canvas id="triangle" width="400" height="400"></canvas>