Question

I'am very new at this and I'm trying to create a signature drawing program in html, canvas and javascript.

Im trying to get the clear button working with this function;

function clearCanvas() {
   var canvas = document.getElementById('canvas');
   var context = canvas.getContext('2d');
   context.clearRect(0, 0, canvas.width, canvas.height);

But it does not seem to work. I don't really know where in the js script to put the function for it to be executed in the html code.

this is the html code:

<!DOCTYPE html>
<html lang="sv">
  <head>
    <meta charset="utf-8">
    <script type="text/javascript" src="uppgift-6.js"></script>
    <title>Uppgift6</title>
    <style type="text/css">
      #canvas { position: relative; }
      #bildruta { border: 2px solid #000; }
      body {font-family: Calibri}
      h2 {font-size: 150%; color: BLACK; background-color: BEIGE; padding:  20px; margin: 5px auto; text-align: center;}
    </style>
  </head>
  <body>
    <h2>Signatur</h2>
    <div id="canvas">
      <canvas id="bildruta" width="600" height="400"></canvas>
    </div>
    <button type="button" onclick="clearCanvas()"> Clear signature </button>
  </body>
</html>

Grateful for all help that i can get!

Answer 1

您的ID不正确。更改您的ID或更改JS行：

function clearCanvas() {
   var canvas = document.getElementById('bildruta'); // that's the correct ID
   var context = canvas.getContext('2d');
   context.clearRect(0, 0, canvas.width, canvas.height);
}

它有效。

Answer 2

var canvas = document.getElementById('canvas')指向此div <div id="canvas">而不是你的画布。它应该是document.getElementById('bildruta')

Clear button not working with my javascript and hmtl5 canvas

2 个答案: