I have put text on an image in a <canvas> tag (the text was taken from an input box). Now if I put a new text on the <canvas> , it is imposed on the previous text. How do I clear the existing text on the canvas before putting in the new text? I have tried resetting the canvas by assigning canvas.width but the text stays on. Any help people?

How do I clear text from the <canvas> element?

Here is the best approach and it worked for me. Clear function is just to clear the recaptcha. So just call this function when you refresh.

    <!DOCTYPE html>
<html>
<head>
    <meta charset='utf-8'>
    <meta http-equiv='X-UA-Compatible' content='IE=edge'>
    <title>Page Title</title>
    <meta name='viewport' content='width=device-width, initial-scale=1'>
    <link rel='stylesheet' type='text/css' media='screen' href='main.css'>
    <script src='main.js'></script>
</head>
<body>
<h4>Canvas</h4><canvas width="200" height="100" id="cnv1"></canvas><br/>
<button id="clear_cnv">Clear</button> - <button id="setnr_cnv">Set Nr</button>
<script type="text/javascript">
// <![CDATA[
// function to clear the canvas ( https://coursesweb.net/ )
// cnv = the object with the canvas element
function clearCanvas(cnv) {
  var ctx = cnv.getContext('2d');     // gets reference to canvas context
  ctx.beginPath();    // clear existing drawing paths
  ctx.save();         // store the current transformation matrix

  // Use the identity matrix while clearing the canvas
  ctx.setTransform(1, 0, 0, 1, 0, 0);
  ctx.clearRect(0, 0, cnv.width, cnv.height);

  ctx.restore();        // restore the transform
}

// sets and adds a random number in canvas
// cnv = the object with the canvas element
function  addNrCnv(cnv) {
  // gets a random number between 1 and 100
  var nr =  Math.floor(Math.random() * 100 + 1);

  var ctx = cnv.getContext('2d');     // gets reference to canvas context

  // create text with the number in canvas (sets text color, font type and size)
  ctx.fillStyle = '#00f';
  ctx.font = 'italic 38px sans-serif';
  ctx.fillText(nr, 80, 64);
}

// get a reference to the <canvas> tag
var cnv1 = document.getElementById('cnv1');

// register onclick event for #clear_cnv button to call the clearCanvas()
document.getElementById('clear_cnv').onclick = function() { clearCanvas(cnv1); }

// register onclick event for #setnr_cnv button to call the addNrCnv()
document.getElementById('setnr_cnv').onclick = function() { addNrCnv(cnv1); }
// ]]>
</script>
</body>
</html>

How do I clear text from the <canvas> element?

7 Answers