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I'm playing with HTML5 canvas element with JavaScript. Now I can draw shapes to the canvas with internal JavaScript when I create an external file I get an Uncaught Type Error. All I want to do is draw a rectangle to my canvas through an external file.

Here is my HTML:

<!DOCTYPE HTML>
<html lang="en">

<head>
    <meta charset="utf-8">
    <title>FireBlaster</title>
</head>

<body style="background:#111111">
    <div id="inner">
        <button id="drawSquareBtn" type="button">Draw Square</button>
        <canvas id="myCanvas" width="600px" ; height="400px;" style=" dispaly:block; background:#000000; margin:8% 25%;"></canvas>
    </div>
    <script type="text/javascript" src="game.js"></script>
</body>

</html>

This is my JavaScript:

//JavaScript Document
var canvasBg = document.getElementById('myCanvas');
var ctx = canvasBg.getContext('2D');

function drawSquare() {

    alert('your pressed a button!');
    ctx.fillStyle = "#0A0AFF";
    ctx.fillRect(200, 150, 150, 50);
}
var drawSquareBtn = document.getElementById('drawSquareBtn');
drawSquareBtn.addEventListener('click', drawSquare, false);

I'm playing with HTML5 canvas element with JavaScript. Now I can draw shapes to the canvas with internal JavaScript when I create an external file I get an Uncaught Type Error. All I want to do is draw a rectangle to my canvas through an external file.

Here is my HTML:

<!DOCTYPE HTML>
<html lang="en">

<head>
    <meta charset="utf-8">
    <title>FireBlaster</title>
</head>

<body style="background:#111111">
    <div id="inner">
        <button id="drawSquareBtn" type="button">Draw Square</button>
        <canvas id="myCanvas" width="600px" ; height="400px;" style=" dispaly:block; background:#000000; margin:8% 25%;"></canvas>
    </div>
    <script type="text/javascript" src="game.js"></script>
</body>

</html>

This is my JavaScript:

//JavaScript Document
var canvasBg = document.getElementById('myCanvas');
var ctx = canvasBg.getContext('2D');

function drawSquare() {

    alert('your pressed a button!');
    ctx.fillStyle = "#0A0AFF";
    ctx.fillRect(200, 150, 150, 50);
}
var drawSquareBtn = document.getElementById('drawSquareBtn');
drawSquareBtn.addEventListener('click', drawSquare, false);
  • javascript
  • html
  • canvas
  • methods
  • typeerror
Share Improve this question edited Mar 18, 2018 at 1:08 sg7 6,2982 gold badges34 silver badges41 bronze badges asked Dec 24, 2012 at 14:30 MattyMatty 151 gold badge2 silver badges8 bronze badges
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2 Answers 2

Reset to default 3

The d in getContext("2d") needs to be lower case.

Live Demo

// Changed d to lower case
var ctx = canvasBg.getContext('2d');

Wrong : -- var ctx = canvasBg.getContext('2D');

Right :-- var ctx = canvasBg.getContext('2d');

D capital does not create instance.

本文标签： htmlUncaught Type Error Cannot set property of 39fillStyle39 of null HTML5 JavascriptStack Overflow

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