Even though this is becoming less and less of a problem, some devices or browsers may still not support WebGL. The following method allows you to check if it is supported and display a message to the user if it is not.
Add [link:https://github.com/mrdoob/three.js/blob/master/examples/jsm/WebGL.js] to your javascript and run the following before attempting to render anything.
if ( WEBGL.isWebGLAvailable() ) {
// Initiate function or other initializations here
animate();
} else {
var warning = WEBGL.getWebGLErrorMessage();
document.getElementById( 'container' ).appendChild( warning );
}