Resize HTML5 canvas to fit window

How can I automatically scale the HTML5 <canvas> element to fit the page?

For example, I can get a <div> to scale by setting the height and width properties to 100%, but a <canvas> won't scale, will it?

I believe I have found an elegant solution to this:

JavaScript

/* important! for alignment, you should make things
 * relative to the canvas' current width/height.
 */
function draw() {
  var ctx = (a canvas context);
  ctx.canvas.width  = window.innerWidth;
  ctx.canvas.height = window.innerHeight;
  //...drawing code...
}

CSS

html, body {
  width:  100%;
  height: 100%;
  margin: 0;
}

Hasn't had any large negative performance impact for me, so far.

The following solution worked for me the best. Since I'm relatively new to coding, I like to have visual confirmation that something is working the way I expect it to. I found it at the following site: http://htmlcheats.com/html/resize-the-html5-canvas-dyamically/

Here's the code:

(function() {
  var
    // Obtain a reference to the canvas element using its id.
    htmlCanvas = document.getElementById('c'),
    // Obtain a graphics context on the canvas element for drawing.
    context = htmlCanvas.getContext('2d');

  // Start listening to resize events and draw canvas.
  initialize();

  function initialize() {
    // Register an event listener to call the resizeCanvas() function 
    // each time the window is resized.
    window.addEventListener('resize', resizeCanvas, false);
    // Draw canvas border for the first time.
    resizeCanvas();
  }

  // Display custom canvas. In this case it's a blue, 5 pixel 
  // border that resizes along with the browser window.
  function redraw() {
    context.strokeStyle = 'blue';
    context.lineWidth = '5';
    context.strokeRect(0, 0, window.innerWidth, window.innerHeight);
  }

  // Runs each time the DOM window resize event fires.
  // Resets the canvas dimensions to match window,
  // then draws the new borders accordingly.
  function resizeCanvas() {
    htmlCanvas.width = window.innerWidth;
    htmlCanvas.height = window.innerHeight;
    redraw();
  }
})();

html,
body {
  width: 100%;
  height: 100%;
  margin: 0px;
  border: 0;
  overflow: hidden;
  /*  Disable scrollbars */
  display: block;
  /* No floating content on sides */
}

<canvas id='c' style='position:absolute; left:0px; top:0px;'></canvas>

The blue border shows you the edge of the resizing canvas, and is always along the edge of the window, visible on all 4 sides, which was NOT the case for some of the other above answers. Hope it helps.

Resize HTML5 canvas to fit window

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