Sketch.js Copy the canvas to clipboard - javascript

I'm currently trying to make a solution, which needs me to be able to draw on top of a image.
I'm using sketch.js.
The problem is i need to copy the Base64 image instead of viewing it. So i can paste it into another program.
Is there any solution for this?
EDIT: The code is a website with one background, and sketch.js to draw lines on top of the background. Then i want to save the picture created in my clipboard, either the image or the base64 code.
<!doctype html>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<script src="https://code.jquery.com/jquery-2.1.1.min.js"></script>
<script src="https://rawgit.com/intridea/sketch.js/gh-pages/lib/sketch.js"></script>
<style>
body{ background-color: white; }
#wrapper{positon:relative;}
#bk,#myCanvas{position:absolute;}
</style>
<script>
$(function(){
var c = document.getElementById("myCanvas");
var ctx = c.getContext("2d");
$('#myCanvas').sketch({ defaultColor: "red" });
$('#download').click(function() {
var img=document.getElementById('bk');
ctx.globalCompositeOperation='destination-over';
ctx.drawImage(bk, 0, 0);
ctx.globalCompositeOperation='source-over';
var html="";
html+="<img src='"+c.toDataURL()+"' alt='from canvas'/>";
var tab=window.open();
tab.document.write(html);
});
}); // end $(function(){});
</script>
</head>
<body>
<h4>Hold to draw.</h4>
<button id=download>Save picture</button>
<div id="SketchTools">
<!-- Basic tools -->
<img src="img/black_icon.png" alt="Black"/>
<img src="img/red_icon.png" alt="Red"/>
<img src="img/green_icon.png" alt="Green"/>
<br/>
<!-- Size options -->
<img src="img/pencil_icon.png" alt="Pencil"/>
<img src="img/pen_icon.png" alt="Pen"/>
<img src="img/stick_icon.png" alt="Stick"/>
<img src="img/smallbrush_icon.png" alt="Small brush"/>
<img src="img/mediumbrush_icon.png" alt="Medium brush"/>
<img src="img/bigbrush_icon.png" alt="Big brush"/>
<img src="img/bucket_icon.png" alt="Huge bucket"/>
<br/>
</div>
<div id='wrapper'>
<img crossOrigin='anonymous' id=bk src='picturehere'>
<canvas id="myCanvas" width=800 height=600></canvas>
</div>
</body>
</html>


It is simple to copy to the clipboard but it does require user interaction. It can not be done automatically, or the data hidden, as that would pose a significant security risk. That said there is a work around using flash but personally I hope that hole is plugged soon.
So to the solution.
Add a textarea and a button labeled click. The image is copied to the textarea, clicking the button selects the text in the textarea and issue the cut command via document.execCommand('cut'); you could use 'copy' but cut gives some feed back.
I have tried to hide the textarea display:nonebut that blocks the cut, I have tried to issue the click event in code, that also blocked the cut/copy command
// this function is just here to draw a smile and add get the dataURL
// for the demo. It has no relevance to the problem
var smile = function(){
var image = document.createElement("canvas");
image.width = 32;
image.height =32;
var ct = image.getContext("2d"); // tack the context onto the image
var bp = function(){ct.beginPath();}
var p = Math.PI;
var pp = Math.PI*2;
var cx = cy = 16;
var s = function(){ct.stroke();}
var f = function(){ct.fill();}
var a = function(a1,a2,a3){bp(); ct.arc(cx,cy,a1,a2,a3)};
var af = function(a1,a2,a3){bp(); ct.arc(cx,cy,a1,a2,a3);f()};
var b = "black"
var w = "white";
var y = "yellow";
var col = function(a1,a2,a3){ ct.fillStyle = a1;ct.strokeStyle = a2;ct.lineWidth=a3;}
col(b,y);af(16,0,pp);col(y,b,2);af(14,0,pp);a(10,0.2,p-0.2);s();cx = 8;cy = 11;col(b,b,1);af(6,0,pp);col(w,b,1);af(5,0,pp);col(b,b,1);af(2,0,pp);cx = 24;af(6,0,pp);col(w,b,1);af(5,0,pp);col(b,b,1);af(2,0,pp);
// show the URL
imageShow.src = image.toDataURL("image/png");
// add the canvas URL base64 to the text area
textA.textContent = image.toDataURL("image/png");
}
//' get the elements we need
var textA = document.querySelector('#imgDat'); // text area that holds the URL
var imageShow = document.querySelector('#showIt'); // just to show whats being copied
var button = document.querySelector('#copyBut'); // the button to do it all;
smile(); // Create an image display it and put it in textArea
button.addEventListener("click",function(){
textA.select(); // select the content of the textArea
document.execCommand('cut'); // cut the selected content into
// cut/paste buffer
})
<textarea id="imgDat" ></textarea>
<img id="showIt"><input id="copyBut" type="button" value="COPY"><br>
Click to copy image as dataURL to clipboard.
Only Tested on chrome, and hope this helps.

Related

Programmatically setting unique onclicks to imgs in a loop in Javascript

So I have this gallery page where I have multiple <img> tags with a unique picture. Clicking on the picture should take you to a another webpage with more info on that specific picture. Hence, all onclick()s are unique, depending on the src of the image.
Now, given the fact that all these <img> tags are virtually same save for picture, I decided to use JavaScript to make all of them in a loop, as seen below:
loadImageGalleryData
for (var i = 0; i < 21; i++) {
var imgSrc = "http://localhost:63342/Performance%20Task/Website/imgs/gallery/img/" + i + ".jpg";
console.log(imgSrc);
var imgDiv = document.createElement('div');
imgDiv.className = "img";
var descDiv = document.createElement('div');
descDiv.className = "desc";
var imgView = document.createElement('img');
imgView.src = imgSrc;
imgView.onclick = (function() {{openWebpage(imgSrc);}})();
console.log(imgSrc);
imgView.width = 300;
imgView.height = 200;
imgDiv.appendChild(imgView);
imgDiv.appendChild(descDiv);
document.getElementsByTagName('body')[0].appendChild(imgDiv);
}
The openWebpage() function in particular is this one:
openWebpage()
function openWebpage(src) {
var orig = window.document.title;
window.document.title = src;
open("imagePage.html");
}
The imagePage has a jscript which tells ITS OWN img and div tag to display the image, whose source is received from window.document.opener.title or somethign like that.
All the images get built, but the onclick() doesn't register. A peek in the developer mode in Chrome, and the images don't have an onlick() attribute.
Also, if I change this snippet of code:
imgView.onclick = (function() {{openWebpage(imgSrc);}})();
into this:
imgView.onclick = function() {openWebpage(imgSrc);};
The onlick() DOES register, but for every image simultaneously, with the src of the last image created. So when I click on Picture 1, it goes to the information of Picture 22. Same goes for every other picture. It's all the same info.
What am I doing wrong here?
EDIT: ADDITIONAL INFO
imagePage.html
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<link rel="stylesheet" href="css/imagePage.css"/>
<script src="jscript/imageData.js"></script>
<script src="jscript/loadImageData.js"></script>
</head>
<ul>
<li>Home</li>
<li>Gallery</li>
<li>About</li>
<li>Contact</li>
</ul>
<body>
<div>
<h1 id="imageTitle">TESTTITLE</h1>
</div>
<div>
<img id="imageView">
</div>
<div class="boxed" id="imageDesc">
</div>
</body>
</html>
loadImageData
window.onload = function() {
var imageSrc = opener.document.title;
var imageDesc = map[imageSrc];
var imageView = document.getElementById("imageView");
var imageDescView = document.getElementById("imageDesc");
imageView.src = imageSrc;
imageDescView.innerHTML = imageDesc;
};

On the last iteration of your loop, you set imgSrc to the url of picture 22. So on the click event your function openWebPage fires with that url in the argument.

Try this.
imgView.addEventListener("click", function() {openWebpage(imgSrc);});

Add Links to Images in a Script

This script replaces the background of the DIV 'middle' with the images listed in the array. Currently the script works perfect but I want to be able to assign a link to each image, tried just replacing with but then the image doesn't show up nor does the link work.
<script>
var images=new Array('/images/home/imgone.jpg', '/images/home/imgtwo.jpg', '/images/home/imgthree.jpg', '/images/home/imgfour.jpg', '/images/home/imgfive.jpg');
var nextimage=0;
doSlideshow();
function doSlideshow(){
if(nextimage>=images.length){nextimage=0;}
$('.middle')
.css('background-image','url("'+images[nextimage++]+'")')
.fadeIn(500,function(){
setTimeout(doSlideshow,5000);
});
}
</script>
What I'm looking for is something like this.
<script>
var images=new Array('/images/home/imgone.jpg', '/images/home/imgtwo.jpg', '/images/home/imgthree.jpg', '/images/home/imgfour.jpg', '/images/home/imgfive.jpg'); To: var images=new Array('<img src="/images/home/imgone.jpg"', '<img src="/images/home/imgtwo.jpg"', '<img src="/images/home/imgthree.jpg"', '<img src="/images/home/imgfour.jpg"', '<img src="/images/home/imgfive.jpg"');
</script>

Although this does not fully answer your question, maybe you can get some ideas from DOM functions.
Example
<script>
// Creates Image
var image = document.createElement("img");
// Sets Image Attributes
image.src = "http://i.imgur.com/gqdqudn.png";
image.width = "30";
image.height = "30";
// Adds Image to Body
document.body.appendChild(image);
</script>
This appends an image to the body. If you would like to add it to a specific ID, you could do the following (assuming your div id is "destination").
Example
<!DOCTYPE html>
<html>
<body>
<div id="destination">
<!-- Destination Div -->
</div>
<script>
// Creates Image
var image = document.createElement("img");
// Sets Image Attributes
image.src = "http://i.imgur.com/gqdqudn.png";
image.width = "30";
image.height = "30";
// Adds Image to Body
document.getElementById("destination").appendChild(image);
</script>
</body>
</html>
Good luck!

Displaying a Box on an HTML page using external Javascript?

When a submit button is clicked on an HTML page a box should display anywhere on the page of any color also. I am using an external JavaScript page to accomplish this. However, it isn't working... I tried to debug it and it wont get past the point of var body = document.getElementsById("body")[0];
Here is the HTML code:
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>Exercise 2 - Question 2</title>
<script src="E02_Q2.js"></script>
</head>
<body>
<form>
<input type="submit" value="Add Box" onclick="ShowBox()"/>
</form>
</body>
</html>
Here is the External Javascript to accompany it:
function ShowBox(){
//get the body element of the document
var body = document.getElementsById("body")[0];
//create the canvas tag
var canvas = document.createElement("canvas");
canvas.height = 200;
canvas.width = 200;
var context = canvas.getContext("2d");
//create the box and append onto the canvas
canvas.fillStyle = "#FF0000";
canvas.fillRect(50,50,100,100);
//append the canvas onto the body
body.appendChild(canvas);
}
Not quite sure where i'm going wrong here...

First, There is a mistake in the below line. (You don't have any element with id as body and even if there had been an element with id='body' the method is not getElementsById, it should be getElementById.)
var body = document.getElementsById("body")[0];
Instead it should be like below using getElementsByTagName
var body = document.getElementsByTagName("body")[0];
Second, fillStyle and fillRect should be on context and not canvas.
context.fillStyle = "#FF0000";
context.fillRect(50,50,100,100);
Third, you have to return false; to prevent the default action of the submit button like below:
<input type="submit" value="Add Box" onclick="ShowBox();return false;"/>
Fiddle

Change form button to normal button. Otherwise add return false in the function.
<form>
<input type="button" value="Add Box" onclick="ShowBox()"/>
</form>
There are more errors in the function., please check the script below.
Eg : http://jsfiddle.net/3EwxB/
function ShowBox(){
var body = document.getElementsByTagName("body")[0];
//create the canvas tag
var canvas = document.createElement("canvas");
canvas.height = 200;
canvas.width = 200;
var context = canvas.getContext("2d");
//create the box and append onto the canvas
context.fillStyle = "#FF0000";
context.fillRect(50,50,100,100);
//append the canvas onto the body
body.appendChild(canvas);
}

How to save an image from canvas

Recently I've been attempting to create a photo booth by relying on Webrtc and have nearly completed all of the code except I've not been able to figure out a way to save the image after it has been captured.
This is the closest I've come so far to achieving my goal:
<meta charset="UTF-8" />
<meta http-equiv="X-UA-Compatible" content="IE=edge,chrome=1" />
<title>fotogoof</title>
<link rel="Stylesheet" href="css/bootstrap.css"/>
<link rel="Stylesheet" href="css/style.css"/>
<script type="text/javascript">
window.onload = function () {
var img = document.getElementById('screenshot');
var button = document.getElementById('saveImage');
img.src = '';
img.onload = function () {
button.removeAttribute('disabled');
};
button.onclick = function () {
window.location.href = img.src.replace('image/png', 'image/octet-stream');
};
};
</script>
</head>
<div class="navbar navbar-inverse navbar-fixed-top">
<div class="navbar-inner">
<div class="container">
<h2 class="brand">Html5 Photobooth</h1>
</div>
</div>
</div>
<div class="container" id="body-wrap">
<div class="container" id="main">
<div class="span10">
<div id="video-container">
<canvas width="400" height="320" class="mask"></canvas>
<div id="counter">
</div>
</div>
<br><div id="pic-holder" class="pull-left"><img id="screenshot"></div></br>
<input id="saveImage" type="button" value="save image" disabled="disabled"/>
</div>
</div>
</div>
</div>
The code is essentially taking the webcam stream and feeding it into a canvas element. Pressing the space button triggers a screenshot to be taken, which then appears as an image. Because I'm unable to provide the exact source of the file that is being downloaded the button only opens the image in another tab in the browser instead of functioning properly. I would really appreciate some input as to how I can resolve this. Thanks in advance.
I've already managed to do capture the stream from the canvas in an image with this bit of code:
document.addEventListener ('keydown', function (event) {
if(event.keyCode == 32) {
document.querySelector('#screenshot').src = canvas.toDataURL('image/webp')
}
})
What I want to know is how to enable the user to save the image onto their computer from there.

If I understand correctly you want to download (ie. provide a save dialog for the user to pick a location) the image to user's machine?'
If so you can use this snippet:
function download(canvas, filename) {
/// create an "off-screen" anchor tag
var lnk = document.createElement('a'),
e;
/// the key here is to set the download attribute of the a tag
lnk.download = filename;
/// convert canvas content to data-uri for link. When download
/// attribute is set the content pointed to by link will be
/// pushed as "download" in HTML5 capable browsers
lnk.href = c.toDataURL();
/// create a "fake" click-event to trigger the download
if (document.createEvent) {
e = document.createEvent("MouseEvents");
e.initMouseEvent("click", true, true, window,
0, 0, 0, 0, 0, false, false, false,
false, 0, null);
lnk.dispatchEvent(e);
} else if (lnk.fireEvent) {
lnk.fireEvent("onclick");
}
}
Now all you need to do is to provide a default file name and call the function:
download(myCanvas, 'untitled.png');
If you rather than this mean save directly to user's harddisk then you can't due to security reasons.
That being said, there is always the option of using local storage such as File API or Indexed DB - but as these are sand-boxed you and the user will only have access to the "files" through the browser so perhaps not so convenient.

I don't think it's possible for IE without involving a server side script. Here's a good writeup on how to do it that way.

I had this problem and this is the best solution without any external or additional script libraries:
In Javascript tags or file create this function:
We assume here that canvas is your canvas:
function download(){
var download = document.getElementById("download");
var image = document.getElementById("canvas").toDataURL("image/png")
.replace("image/png", "image/octet-stream");
download.setAttribute("href", image);
}
In the body part of your HTML specify the button:
<a id="download" download="image.png"><button type="button" onClick="download()">Download</button></a>
This is working and download link looks like a button.

Regarding the first task, you can export the canvas content to an image with toDataUrl method supported by the canvas object.
var canvas = document.getElementById("canvas");
if (canvas.getContext) {
var ctx = canvas.getContext("2d"); // Get the context for the canvas.
var myImage = canvas.toDataURL("image/png"); // Get the data as an image.
}
var image = document.getElementById("screenshot"); // Get the image object.
image.src = myImage;

how to save canvas as png image?

I have a canvas element with a drawing in it, and I want to create a button that when clicked on, it will save the image as a png file. So it should open up the save, open, close dialog box...
I do it using this code
var canvas = document.getElementById("myCanvas");
window.open(canvas.toDataURL("image/png"));
But when I test it out in IE9, a new window opens up saying "the web page cannot be displayed"
and the url of it is:
data:image/png;base64,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
Anyone know how to fix this?

try this:
var canvas = document.getElementById("alpha");
var dataURL = canvas.toDataURL("image/png");
var newTab = window.open('about:blank','image from canvas');
newTab.document.write("<img src='" + dataURL + "' alt='from canvas'/>");
This shows image from canvas on new page, but if you have open popup in new tab setting it shows about:blank in address bar.
EDIT:- though window.open("<img src='"+ canvas.toDataURL('image/png') +"'/>") does not work in FF or Chrome, following works though rendering is somewhat different from what is shown on canvas, I think transparency is the issue:
window.open(canvas.toDataURL('image/png'));

FileSaver.js should be able to help you here.
var canvas = document.getElementById("my-canvas");
// draw to canvas...
canvas.toBlob(function(blob) {
saveAs(blob, "pretty image.png");
});

To accomodate all three points:
button
save the image as a png file
open up the save, open, close dialog box
The file dialog is a setting in the browser.
For the button/save part assign the following function, boiled down from other answers, to your buttons onclick:
function DownloadCanvasAsImage(){
let downloadLink = document.createElement('a');
downloadLink.setAttribute('download', 'CanvasAsImage.png');
let canvas = document.getElementById('myCanvas');
let dataURL = canvas.toDataURL('image/png');
let url = dataURL.replace(/^data:image\/png/,'data:application/octet-stream');
downloadLink.setAttribute('href', url);
downloadLink.click();
}
Example on Codepen
Another, somewhat cleaner, approach is using Canvas.toBlob():
function DownloadCanvasAsImage(){
let downloadLink = document.createElement('a');
downloadLink.setAttribute('download', 'CanvasAsImage.png');
let canvas = document.getElementById('myCanvas');
canvas.toBlob(function(blob) {
let url = URL.createObjectURL(blob);
downloadLink.setAttribute('href', url);
downloadLink.click();
});
}
Example on Codepen
Neither solution is 100% cross browser compatible, so check the client

I used this solution to set the file name:
HTML:
Download!
<canvas id="canvas"></canvas>
JavaScript:
function download(){
document.getElementById("downloader").download = "image.png";
document.getElementById("downloader").href = document.getElementById("canvas").toDataURL("image/png").replace(/^data:image\/[^;]/, 'data:application/octet-stream');
}

I had this problem and this is the best solution without any external or additional script libraries:
In Javascript tags or file create this function:
We assume here that canvas is your canvas:
function download(){
var download = document.getElementById("download");
var image = document.getElementById("canvas").toDataURL("image/png")
.replace("image/png", "image/octet-stream");
download.setAttribute("href", image);
}
In the body part of your HTML specify the button:
<a id="download" download="image.png"><button type="button" onClick="download()">Download</button></a>
This is working and download link looks like a button. Tested in Firefox and Chrome.

I maybe discovered a better way for not forcing the user to right click and "save image as". Live draw the canvas base64 code into the href of the link and modify it so the download will start automatically. I don't know if it's universally browser compatible, but it should work with the main/new browsers.
var canvas = document.getElementById('your-canvas');
if (canvas.getContext) {
var C = canvas.getContext('2d');
}
$('#your-canvas').mousedown(function(event) {
// feel free to choose your event ;)
// just for example
// var OFFSET = $(this).offset();
// var x = event.pageX - OFFSET.left;
// var y = event.pageY - OFFSET.top;
// standard data to url
var imgdata = canvas.toDataURL('image/png');
// modify the dataUrl so the browser starts downloading it instead of just showing it
var newdata = imgdata.replace(/^data:image\/png/,'data:application/octet-stream');
// give the link the values it needs
$('a.linkwithnewattr').attr('download','your_pic_name.png').attr('href',newdata);
});
You can wrap the <a> around anything you want.

Submit a form that contains an input with value of canvas toDataURL('image/png') e.g
//JAVASCRIPT
var canvas = document.getElementById("canvas");
var url = canvas.toDataUrl('image/png');
Insert the value of the url to your hidden input on form element.
//PHP
$data = $_POST['photo'];
$data = str_replace('data:image/png;base64,', '', $data);
$data = base64_decode($data);
file_put_contents("i". rand(0, 50).".png", $data);

Try this:
jQuery('body').after('<a id="Download" target="_blank">Click Here</a>');
var canvas = document.getElementById('canvasID');
var ctx = canvas.getContext('2d');
document.getElementById('Download').addEventListener('click', function() {
downloadCanvas(this, 'canvas', 'test.png');
}, false);
function downloadCanvas(link, canvasId, filename) {
link.href = document.getElementById(canvasId).toDataURL();
link.Download = filename;
}
You can just put this code in console in firefox or chrom and after changed your canvas tag ID in this above script and run this script in console.
After the execute this code you will see the link as text "click here" at bottom of the html page. click on this link and open the canvas drawing as a PNG image in new window save the image.

Full Working HTML Code. Cut+Paste into new .HTML file:
Contains Two Examples:
Canvas in HTML file.
Canvas dynamically created with Javascript.
Tested In:
Chrome
Internet Explorer
*Edge (title name does not show up)
Firefox
Opera
<!DOCTYPE HTML >
<html lang="en">
<head>
<meta charset="UTF-8">
<title> #SAVE_CANVAS_TEST# </title>
<meta
name ="author"
content="John Mark Isaac Madison"
>
<!-- EMAIL: J4M4I5M7 -[ＡＴ]- Hotmail.com -->
</head>
<body>
<div id="about_the_code">
Illustrates:
<ol>
<li>How to save a canvas from HTML page. </li>
<li>How to save a dynamically created canvas.</li>
</ol>
</div>
<canvas id="DOM_CANVAS"
width ="300"
height="300"
></canvas>
<div id="controls">
<button type="button" style="width:300px;"
onclick="obj.SAVE_CANVAS()">
SAVE_CANVAS ( Dynamically Made Canvas )
</button>
<button type="button" style="width:300px;"
onclick="obj.SAVE_CANVAS('DOM_CANVAS')">
SAVE_CANVAS ( Canvas In HTML Code )
</button>
</div>
<script>
var obj = new MyTestCodeClass();
function MyTestCodeClass(){
//Publically exposed functions:
this.SAVE_CANVAS = SAVE_CANVAS;
//:Private:
var _canvas;
var _canvas_id = "ID_OF_DYNAMIC_CANVAS";
var _name_hash_counter = 0;
//:Create Canvas:
(function _constructor(){
var D = document;
var CE = D.createElement.bind(D);
_canvas = CE("canvas");
_canvas.width = 300;
_canvas.height= 300;
_canvas.id = _canvas_id;
})();
//:Before saving the canvas, fill it so
//:we can see it. For demonstration of code.
function _fillCanvas(input_canvas, r,g,b){
var ctx = input_canvas.getContext("2d");
var c = input_canvas;
ctx.fillStyle = "rgb("+r+","+g+","+b+")";
ctx.fillRect(0, 0, c.width, c.height);
}
//:Saves canvas. If optional_id supplied,
//:will save canvas off the DOM. If not,
//:will save the dynamically created canvas.
function SAVE_CANVAS(optional_id){
var c = _getCanvas( optional_id );
//:Debug Code: Color canvas from DOM
//:green, internal canvas red.
if( optional_id ){
_fillCanvas(c,0,255,0);
}else{
_fillCanvas(c,255,0,0);
}
_saveCanvas( c );
}
//:If optional_id supplied, get canvas
//:from DOM. Else, get internal dynamically
//:created canvas.
function _getCanvas( optional_id ){
var c = null; //:canvas.
if( typeof optional_id == "string"){
var id = optional_id;
var d = document;
var c = d.getElementById( id );
}else{
c = _canvas;
}
return c;
}
function _saveCanvas( canvas ){
if(!window){ alert("[WINDOW_IS_NULL]"); }
//:We want to give the window a unique
//:name so that we can save multiple times
//:without having to close previous
//:windows.
_name_hash_counter++ ;
var NHC = _name_hash_counter ;
var URL = 'about:blank' ;
var name= 'UNIQUE_WINDOW_ID' + NHC;
var w=window.open( URL, name ) ;
if(!w){ alert("[W_IS_NULL]");}
//:Create the page contents,
//:THEN set the tile. Order Matters.
var DW = "" ;
DW += "<img src='" ;
DW += canvas.toDataURL("image/png");
DW += "' alt='from canvas'/>" ;
w.document.write(DW) ;
w.document.title = "NHC"+NHC ;
}
}//:end class
</script>
</body>
<!-- In IE: Script cannot be outside of body. -->
</html>

I really like Tovask's answer but it doesn't work due to the function having the name download (this answer explains why). I also don't see the point in replacing "data:image/..." with "data:application/...".
The following code has been tested in Chrome and Firefox and seems to work fine in both.
JavaScript:
function prepDownload(a, canvas, name) {
a.download = name
a.href = canvas.toDataURL()
}
HTML:
Download
<canvas id="canvasId"></canvas>

My solution via vue and async support
async downloadImage () {
const canvas = this.$refs.canvas
const blob = await new Promise(resolve => canvas.toBlob(resolve))
const downloadLink = document.createElement('a')
downloadLink.href = window.URL.createObjectURL(blob)
downloadLink.download = 'mycanvasimage.png'
downloadLink.click()
}

var canvasId = chart.id + '-canvas';
var canvasDownloadId = chart.id + '-download-canvas';
var canvasHtml = Ext.String.format('<canvas id="{0}" width="{1}" height="{2}"></canvas><a id="{3}"/>',
canvasId,
chart.getWidth(),
chart.getHeight(),
canvasDownloadId);
var canvasElement = reportBuilder.add({ html: canvasHtml });
var canvas = document.getElementById(canvasId);
var canvasDownload = document.getElementById(canvasDownloadId);
canvasDownload.href = chart.getImage().data;
canvasDownload.download = 'chart';
canvasDownload.click();

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