'Matrix-style' Rainshower

Insert the canvas tag into your html file

<canvas id="c"></canvas>
  						

Next, write your javascript out in a separate file

var c = document.getElementById("c");
var ctx = c.getContext("2d");

//making the canvas full screen
c.height = window.innerHeight;
c.width = window.innerWidth;

//numeric characters - taken from the unicode charset
var numbers = "0123456789";
//converting the string into an array of single characters
numbers = numbers.split("");

var font_size = 10;
var columns = c.width/font_size; //number of columns for the rain
//an array of drops - one per column
var drops = [];
//x below is the x coordinate
//1 = y co-ordinate of the drop(same for every drop initially)
for(var x = 0; x <columns; x++)
	drops[x] = 1; 

//drawing the characters
function draw()
{
	//Black BG for the canvas
	//translucent BG to show trail
	ctx.fillStyle = "rgba(0, 0, 0, 0.05)";
	ctx.fillRect(0, 0, c.width, c.height);
	
	ctx.fillStyle = "#0F0"; //green text
	ctx.font = font_size + "px arial";
	//looping over drops
	for(var i = 0; i < drops.length; i++)
	{
		//a random numeric character to print
		var text = numbers[Math.floor(Math.random()*numbers.length)];
		//x = i*font_size, y = value of drops[i]*font_size
		ctx.fillText(text, i*font_size, drops[i]*font_size);
		
		//sending the drop back to the top randomly after it has crossed the screen
		//adding a randomness to the reset to make the drops scattered on the Y axis
		if(drops[i]*font_size > c.height && Math.random() > 0.975)
			drops[i] = 0;
		
		//incrementing Y coordinate
		drops[i]++;
	}
}

setInterval(draw, 33);
  						

Lastly, attach your javascript files to your page

<script src="http://ajax.googleapis.com/ajax/libs/jquery/1.9.1/jquery.min.js"></script>
<script src="js/matrix.js"></script>