HTML5 -Beginners - functionInsideFunction.html

<!DOCTYPE html>
<html>
<head>
  <meta charsetp="UTF-8">
  <meta name="viewport" content="width=device-width" />
</head>
<body bgcolor="black">
<style>#myCanvas {touch-action: none;}</style>
<canvas id="myCanvas" width="320" height="240" style="border:0px solid #d3d3d3;">
Use different browser.
</canvas>
  <script>
    var c=document.getElementById("myCanvas");
    var ctx=c.getContext("2d");


gameloop=setInterval(doGameLoop,16);

function doGameLoop(){
myCanvas.height = window.innerHeight*.98;
myCanvas.width = window.innerWidth*.96;
ctx.fillStyle="rgb(0,0,0)";
ctx.fillRect(0,0,c.width,c.height);
ctx.fillStyle="rgb(255,255,255)";
ctx.fillText("A javascript/html example.",10,10); 


// create a variable and fill
// it with the return from
// our mainFunction
var a = mainFunction();

ctx.fillText("Our new value : "+a,10,50); 


}
// our main (outer) function
function mainFunction(){
	var retVal = 0;

	// call our inner function
	systemsUpgrade(5);
	
	// this is the function inside
	// a function(inner function)
	function systemsUpgrade(val){
		retVal+=val;
	}
	
	return retVal;
}
</script>
</body>
</html>