一张跨域的图片直接在canvas中使用控制台是会给出警告的：
Error: SecurityError: Failed to execute 'toDataURL' on 'HTMLCanvasElement': Tainted canvases may not be exported.
原因是尽管不通过 CORS 就可以在 canvas 中使用其他来源的图片，但是这会污染画布，并且不再认为是安全的画布，这将可能在 canvas 检索数据过程中引发异常。
如果外部源的内容是 HTML <img> 或 SVG <svg> 元素，会阻止从 canvas 中读取数据。
如果外部源图片是作为 HTMLCanvasElement 或 ImageBitMap 获取的，且图片源不符合同源准则，会阻止读取 canvas 的内容。
解决方式：为图片提供设置 crossorigin 属性
代码：
<!DOCTYPE html> <html lang="zh_CN"> <head> <meta charset="UTF-8" /> <meta http-equiv="X-UA-Compatible" content="IE=edge" /> <meta name="viewport" content="width=device-width, initial-scale=1.0" /> <title>Document</title> </head> <body> <div id="imageBox"></div> <script> let imageURL = "https://cdn.glitch.com/4c9ebeb9-8b9a-4adc-ad0a-238d9ae00bb5%2Fmdn_logo-only_color.svg?1535749917189"; let imageDescription = "The Mozilla logo"; downloadedImg = new Image(); downloadedImg.crossOrigin = "Anonymous"; // 核心代码 downloadedImg.addEventListener("load", imageReceived, false); downloadedImg.alt = imageDescription; downloadedImg.src = imageURL; function imageReceived() { const canvas = document.createElement("canvas"); const context = canvas.getContext("2d");canvas.width = downloadedImg.width; canvas.height = downloadedImg.height; canvas.innerText = downloadedImg.alt;
context.drawImage(downloadedImg, 0, 0); imageBox.appendChild(canvas);
try { localStorage.setItem( "saved-image-example", canvas.toDataURL("image/png") ); } catch (err) { console.error(`Error: ${err}`); } } </script> </body> </html> 标签：canvas,const,downloadedImg,alt,图片,跨域 From： https://www.cnblogs.com/shidawang/p/17236865.html