lineJoin

The lineJoin attribute defines the type of corners where two lines meet. The three valid values are bevel, round, and miter.

example:

function drawLineJoin(context){

  context.strokeStyle = "#000000";
  context.lineWidth = 20;

  context.lineJoin = "bevel";
  context.beginPath();
  context.moveTo(50, 50);
  context.lineTo(300, 50);
  context.lineTo(300, 100);
  context.stroke();
  context.closePath();

  context.lineJoin = "round";
  context.beginPath();
  context.moveTo(50, 150);
  context.lineTo(300, 150);
  context.lineTo(300, 200);
  context.stroke();
  context.closePath();

  context.lineJoin = "miter";
  context.beginPath();
  context.moveTo(50, 250);
  context.lineTo(300, 250);
  context.lineTo(300, 300);
  context.stroke();
  context.closePath();
}