Html5 canvas game(pong) Problem: Uncaught TypeError: Cannot read property 'fillRect' of undefined

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I was in the middle of programming a short pong game(basically ping pong), and I got an error in google chrome it said, Uncaught TypeError: Cannot read property 'fillRect' of undefined
Here is my code:

html:

XML

<!DOCTYPE html>
<html>
<head>
    <title>Pong</title>
</head>
<body>
<canvas id="gameCanvas" width="800" height="600"></canvas>
<script type="text/javascript" src="Pongjs1.js"></script>
</body>
</html>

javascript:

C#

//Pong Game
//================
var canvas, canvasContext;
var ballX = 50;
var ballspeedX = 10;
//================

    window.onload = function() {
        canvas = document.getElementById('gameCanvas');
        canvasContext = canvas.getContext("2d");

        var fps = 30;
        setInterval(function() {
            moveEverything();
            drawEverything();
        }, 1000/fps);
    }
//================
//Movement,physics,etc
//================

    function moveEverything() {
        ballX = ballX + ballspeedX;
        if(ballX >= canvas.width) {
            ballspeedX = -ballspeedX;
        }
        if(ballX <= 0) {
            ballspeedX= -ballspeedX;
        }
    }
//================

    function drawEverything() {


        colourRect(0,0,canvas.width,canvas.height,"black");

        colourRect(0,210,10,100,"white");

        colourRect(ballX,50,10,10,"red");//horizantal,vertical,width,height(IN ORDER)
    }
//================

function colourRect(leftX,TopY,width,height, drawColor) {
    canvasContext.fillStyle = drawColor;
    canvas.Context.fillRect(leftX,topY,width,height);
}

It says the error is on line 28 and 46 in my js file. So the function colourRect and function moveEverything
I have no clue where I went wrong :/ Please check out my code to see where the error is made. Thank you for your time!

Posted 3-May-15 14:16pm

UWStudents

Updated 3-May-15 14:53pm

v2

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Comments

Sergey Alexandrovich Kryukov 3-May-15 20:38pm

"Could not read" sounds gibberish. Exact error information, please. You could looks really bad...
—SA

UWStudents 3-May-15 20:42pm

Ok, I'll check the error in the chrome browser again! Thank you for telling me so soon!

UWStudents 3-May-15 20:43pm

Woops, I did not add the entire error message, my bad. Here is the full one:Uncaught TypeError: Cannot read property 'fillRect' of undefined

Sergey Alexandrovich Kryukov 3-May-15 21:28pm

Oh, now it's clear; thank you for the clarification. Please see my answer.
Also, next time, better don't tell those line numbers. Who will count them? Better describe the error or exception in a comment and then refer to this comment in the text describing a problem.
—SA

UWStudents 3-May-15 21:34pm

Thank you for the information! I will make sure to do that for my next question(s)! Have a good one Sergey!

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Sergey Alexandrovich Kryukov · Accepted Answer · 2015-05-03T15:26:00

This is because Canvas.Content is undefined. There is no such property; and you know it. It should be canvasContent you calculated before as canvas.getContext("2d").

Again, your code is pretty bad. You rely on outer context (this very variable), don't use the power of JavaScript objects, don't use encapsulation, don't use closures, don't even use passing of objects in functions. You create objects in outer scope which you never should use after certain phase of code flow, don't limit scope of variables, and so on.

If you are interested, you can look at couple of my JavaScript articles (one of them is also a Canvas game) where I discuss some of the problems I mentioned above, and their solutions:
Tetris on Canvas,
JavaScript Calculator.

—SA