CanvasRenderingContext2D.isPointInStroke()

isPointInStroke(x, y)
isPointInStroke(path, x, y)

<canvas id="canvas"></canvas>
<p>In stroke: <code id="result">false</code></p>

const canvas = document.getElementById('canvas');
const ctx = canvas.getContext('2d');
const result = document.getElementById('result');

ctx.rect(10, 10, 100, 100);
ctx.stroke();
result.innerText = ctx.isPointInStroke(50, 10);

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

const canvas = document.getElementById('canvas');
const ctx = canvas.getContext('2d');

// Create ellipse
const ellipse = new Path2D();
ellipse.ellipse(150, 75, 40, 60, Math.PI * .25, 0, 2 * Math.PI);
ctx.lineWidth = 25;
ctx.strokeStyle = 'red';
ctx.fill(ellipse);
ctx.stroke(ellipse);

// Listen for mouse moves
canvas.addEventListener('mousemove', function(event) {
  // Check whether point is inside ellipse's stroke
  if (ctx.isPointInStroke(ellipse, event.offsetX, event.offsetY)) {
    ctx.strokeStyle = 'green';
  }
  else {
    ctx.strokeStyle = 'red';
  }

  // Draw ellipse
  ctx.clearRect(0, 0, canvas.width, canvas.height);
  ctx.fill(ellipse);
  ctx.stroke(ellipse);
});