canvas hello world

following tutorial from http://diveintohtml5.info/canvas.html

by Amanda Williamson

HTML

<canvas id="canvas" width="500" height="375"></canvas>

JavaScript

var canvas = document.getElementById("canvas");
var context = canvas.getContext("2d");

for (var x = 0.5; x < 500; x += 10) {
  context.moveTo(x, 0);
  context.lineTo(x, 375);
}

for (var y = 0.5; y < 375; y += 10) {
  context.moveTo(0, y);
  context.lineTo(500, y);
}

context.strokeStyle = "#eee";
context.stroke();

context.beginPath();
context.moveTo(0, 40);
context.lineTo(240, 40);
context.moveTo(260, 40);
context.lineTo(500, 40);
context.moveTo(495, 35);
//arrow end
context.lineTo(500, 40);
context.lineTo(495, 45);

context.moveTo(60, 0);
context.lineTo(60, 153);
context.moveTo(60, 173);
context.lineTo(60, 375);
context.moveTo(65, 370);
context.lineTo(60, 375);
context.lineTo(55, 370);

context.strokeStyle = "#000";
context.stroke();

context.font = "bold 12px sans-serif";
context.fillText("x", 248, 43);
context.fillText("y", 58, 165);

context.textBaseline = "top";
context.fillText("( 0 , 0 )", 8, 5);

context.textAlign = "right";
context.textBaseline = "bottom";
context.fillText("( 500 , 375 )", 492, 370);

//dots
context.fillRect(0, 0, 3, 3);
context.fillRect(497, 372, 3, 3);
 
context.fillStyle = 'green';
context.fillRect(80, 55, 150, 100);