S2JS - Objects: a game with more sprites : Getting started in Javascript

We start with some essentials that hopefully are starting to look familiar:

An HTML header
An HTML canvas
A <SCRIPT> tag to introduce our Javascript

Then, in Javascript land:

A variable called ctx which gives us a drawing context for the canvas
A variable called FPS which holds our frames-per-second rate
A function which will get called for each frame
A timer that calls our function every so-many millseconds

<html> <head> <title> Bat avoiding game using Objects</title> </head> <body> <canvas id="myCanvas" width=300 height=300 style="background:url('/img/etc/night city.png'); background-size: cover"> </canvas> <script> var ctx = myCanvas.getContext("2d"); // Get the drawing context for the canvas var FPS = 40; // How many frames per second function Do_a_Frame () { ctx.clearRect(0, 0, myCanvas.width, myCanvas.height); // clear the background } setInterval(Do_a_Frame, 1000/FPS); // Call our frame renderer every this many milliseconds </script> </body> </html>