function convertImageToCanvas(image) {
// 创建canvas DOM元素，并设置其宽高和图片一样 
let canvas = document.createElement("canvas");
canvas.width = image.width;
canvas.height = image.height;
canvas.getContext("2d").drawImage(image, 0, 0);
// 我们在实际的开发中，需要将抓换后的base64图片编码传输到后台图片服务器，由server直接存储或者生成一张图片；
// 所以会用到 toDataURL
console.log(canvas.toDataURL('image/jpeg'))
return canvas;
}

<div id="d1">
<img style="width: 300px;height: 240px;" src="http://jb51.net/images/cover_thumbnail_3rd.jpg" alt="">
<p>本地未设置跨域允许选项crossorigin=anonymous,web-server未设置跨域允许选项</p>
</div>
<button onclick="setCanvas('d1')">canvas保存</button>

function setCanvas(DOMID) {
let img = document.getElementById(DOMID).querySelector('img')
document.body.appendChild(convertImageToCanvas(img))
}

<div id="d4">
<img style="width: 300px;height: 240px;" src="https://img.alicdn.com/tfs/TB1_uT8a5ERMeJjSspiXXbZLFXa-143-59.png" alt="" crossorigin="anonymous">
<p>本地设置跨域允许选项`crossorigin=anonymous`,`web-server`设置跨域允许选项</p>
</div>
<button onclick="setCanvas('d4')">canvas保存</button>

function setCanvas(DOMID) {
let img = document.getElementById(DOMID).querySelector('img')

img.crossOrigin= 'anonymous'

document.body.appendChild(convertImageToCanvas(img))
}

function setCanvas(DOMID) {
let img = document.getElementById(DOMID).querySelector('img')

img.src =img.src+'?v='+Math.random()
img.crossOrigin= 'anonymous'

img.onload=()=>{
document.body.appendChild(convertImageToCanvas(img))
}
}

let _fabricConfig = {
// ....
crossOrigin:'anonymous'
};
/* fabric对象 */
let _fabricObj = new fabric.Canvas(id, _fabricConfig);


// 新建图片对象时
let imgInstance = new fabric.Image.fromURL(url + '?v='+ Math.random(), img => {}, {crossOrigin: 'anonymous'})

// 动态更新图片时
let currentActive = _fabricInstance.getActiveObj();
currentActive.setSrc(randomURL, img =>{}, {crossOrigin: 'anonymous'})