Using bezierCurveTo

HTML5 canvas demo

HTML

<canvas id="myCanvas" width="600" height="600" />

JavaScript

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

ctx.strokeStyle = 'red';
ctx.lineWidth = 2;

ctx.beginPath();
ctx.moveTo(80,100);
//Define 2 control points and the ending point
ctx.bezierCurveTo(110,100, 150, 80, 138, 50);
//ctx.lineTo(50,40);
ctx.stroke();