javascript - html2canvas Uncaught (in promise) undefined - Stack Overflow

admin管理员组

文章数量:1420939

I have a html tag canvas.

<canvas id="myCanvas"></canvas>

I can draw on it successfully, and it looks really good, as i wanted to be. The problem is on the conversion to png.I use html2canvas for that with Canvas2Image. The html2canvas consoles logs an error: Uncaught (in promise) undefined. Canvas2Image console logs Uncaught (in promise) DOMException: Failed to execute 'drawImage' on 'CanvasRenderingContext2D': The image argument is a canvas element with a width or height of 0. I can understand the error very well, the canvas has width and height != 0. Any ideas?

---

html2canvas code:

    html2canvas(document.getElementById('myCanvas')).then(canvas9 => {

    var theimage9 = Canvas2Image.convertToPNG(canvas9);
    var imageData9 = $(theimage9).attr('src');


    console.log(imageData9);
  });

I have a html tag canvas.

<canvas id="myCanvas"></canvas>

I can draw on it successfully, and it looks really good, as i wanted to be. The problem is on the conversion to png.I use html2canvas for that with Canvas2Image. The html2canvas consoles logs an error: Uncaught (in promise) undefined. Canvas2Image console logs Uncaught (in promise) DOMException: Failed to execute 'drawImage' on 'CanvasRenderingContext2D': The image argument is a canvas element with a width or height of 0. I can understand the error very well, the canvas has width and height != 0. Any ideas?

---

html2canvas code:

    html2canvas(document.getElementById('myCanvas')).then(canvas9 => {

    var theimage9 = Canvas2Image.convertToPNG(canvas9);
    var imageData9 = $(theimage9).attr('src');


    console.log(imageData9);
  });

• javascript
• html
• canvas
• html2canvas

Share Improve this question Follow asked Aug 9, 2018 at 12:50 CacheCache 50122 gold badges55 silver badges1414 bronze badges 1

• Did you ever get this figured out? @Cache – FabricioG Commented Oct 5, 2018 at 19:46

Add a ment  | 

2 Answers 2

Sorted by: Reset to default 2

Tested Chrome, Firefox ok, IE 11 needs adding 2 extra js library to support promise.

function takeSnapShot() {
	html2canvas(document.querySelector("#capture")).then(function(canvas9) {
		var theimage9 = canvas9.toDataURL("image/png");
		document.querySelector("#theimage9").src = theimage9; 
	});
}

<script src="https://cdn.jsdelivr/npm/es6-promise@4/dist/es6-promise.min.js"></script>
<script src="https://cdn.jsdelivr/npm/es6-promise@4/dist/es6-promise.auto.min.js"></script> 
<script src="https://html2canvas.hertzen./dist/html2canvas.min.js"></script>
<div id="capture" style="padding: 10px; background: #f5da55">
    <h4 style="color: #000; ">Hello world!</h4>
</div>
<input type="button" value="Capture" onclick="takeSnapShot()"/>
<img id="theimage9" border="0" />

html2canvas is used for converting html code into a canvas view. If I am understanding correctly, you just want to get an image from the canvas so html2canvas is not needed. Simply just use Canvas2Image on it's own.

Example (blue is the image, red is the canvas):

// Example canvas with circle
var c = document.getElementById("myCanvas");
var ctx = c.getContext("2d");
ctx.beginPath();
ctx.arc(95,50,40,0,2*Math.PI);
ctx.stroke();


var image = Canvas2Image.convertToPNG(c); // Returns HTMLImageElement 

$("#canvasImg").attr('src', image.src); // Set the src of our output image to the src of the HTMLImageElement

<!-- Output -->
<img id="canvasImg" src="" style="border:2px solid blue;">

<!-- Input -->
<canvas id="myCanvas" width="200" height="100" style="border:2px solid red;"></canvas>

<script src="https://ajax.googleapis./ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<script src="https://cdn.jsdelivr/npm/[email protected]/canvas2image.min.js"></script>

本文标签： javascripthtml2canvas Uncaught (in promise) undefinedStack Overflow