How to initialise WebGL

From The WebGL Cookbook

WebGL content is displayed in an HTML canvas element. Use the following code to get a WebGL context for a given canvas.

var gl;
  function initGL(canvas) {
    try {
      gl = canvas.getContext("experimental-webgl");
      gl.viewport(0, 0, canvas.width, canvas.height);
    } catch(e) {
    }
    if (!gl) {
      alert("Could not initialise WebGL, sorry :-(");
    }
  }