We Keep Coding

Access SVG attributes using Fabric.js

I'd like to load a SVG image into canvas using Fabric.js and have access to all attributes of it.
Let's assume I have an image like this:
SVG Image
I tried to it using Fabric.js on 3 ways:
1. (Saved as String) - this method is not loading my image, I took other SVG and attributes can be accessed with svgImg.fill.color property.
fabric.loadSVGFromString(svg, function (objects, options) {
var svgImg = fabric.util.groupSVGElements(objects, options);
canvas.add(svgImg);
});
2. Directly from URL:
fabric.loadSVGFromURL(URLsvg, function (objects, options) {
var svgImg = fabric.util.groupSVGElements(objects, options);
canvas.add(svgImg);
});
3.Using fabric.Image:
<img id="Test_Img" src="~/SVG/homer-simpson.svg" style="display: none;" />
var Img = document.getElementById('Test_Img');
var imgInstance = new fabric.Image(Img, {
left: 90,
top: 80
});
How can I access inner attributes of my SVG and change for example color of Homers T-Shirt?

Loaded SVG objects become groups in fabric.js (if they are not simple geometric forms like a rectangle, circle, etc.).
You can access the members of the group with getObjects(), which returns an array.
Here is a simple example. It reads an SVG consisting of 3 arcs and changes the color of the first arc to blue:
var canvas = new fabric.Canvas('canvas', { preserveObjectStacking: true });
canvas.backgroundColor="#fff";
canvas.renderAll();
fabric.loadSVGFromURL("https://media-public.canva.com/MABtmZU4zXQ/1/screen.svg",function(objects,options) {
var loadedObjects = fabric.util.groupSVGElements(objects, options);
loadedObjects.set({
width: 300,
height: 150
});
canvas.add(loadedObjects);
// Change the first arc to blue
loadedObjects.getObjects()[0].set({fill: "blue"});
canvas.renderAll();
});
It runs with fabric.js Version 3.5.
Working example: https://jsfiddle.net/awehring/k7azLb84/9/

Adding canvas inside another canvas: obj.setCoords is not a function( fabric js)

Started using fabric.js and trying to add a canvas inside another canvas, so that the top canvas stays constant and I'll add objects to inner canvas.
Here is the snippet of adding a canvas to another canvas.
canvas = new fabric.Canvas('artcanvas');
innerCanvas = new fabric.Canvas("innerCanvas");
canvas.add(innerCanvas);
and my html looks like this
<canvas id="artcanvas" width="500" height="500"></canvas>
<canvas id="innerCanvas" width="200" height="200" ></canvas>
Once adding these successfully, what I am going to do is , add the coordinates to the inner canvas, so that it looks like one on another to the end user.
However, ran into the below error for the tried code
Uncaught TypeError: obj.setCoords is not a function
at klass._onObjectAdded (fabric.js:6894)
at klass.add (fabric.js:231)
at main.js:60
at fabric.js:19435
at HTMLImageElement.fabric.util.loadImage.img.onload (fabric.js:754)
_onObjectAdded # fabric.js:6894
add # fabric.js:231
(anonymous) # main.js:60
(anonymous) # fabric.js:19435
fabric.util.loadImage.img.onload # fabric.js:754
Looking at the error message, just went to the line of error and here is what I found in chrome console
Can someone point the mistake in my codes ?

After going through no.of discussions and internet solutions, for time being I am using Fabric Rectangle as a clipper and setting it's boundaries so user can be able to drop/play with in that particular clipper.
Dotted red(image below) is my clipper and now I can bound the dropping and below is the code to add an image with a clipper.
function addImageToCanvas(imgSrc) {
fabric.Object.prototype.transparentCorners = false;
fabric.Image.fromURL(imgSrc, function(myImg) {
var img1 = myImg.set({
left: 20,
top: 20,
width: 460,
height: 460
});
img1.selectable = false;
canvas.add(img1);
var clipRectangle = new fabric.Rect({
originX: 'left',
originY: 'top',
left: 150,
top: 150,
width: 200,
height: 200,
fill: 'transparent',
/* use transparent for no fill */
strokeDashArray: [10, 10],
stroke: 'red',
selectable: false
});
clipRectangle.set({
clipFor: 'layer'
});
canvas.add(clipRectangle);
});
}
Now while appending any image/layer to the canvas, I bind that image/layer/text to the clipper I created.
function addLayerToCanvas(laImg) {
var height = $(laImg).height();
var width = $(laImg).width();
var clickedImage = new Image();
clickedImage.onload = function(img) {
var pug = new fabric.Image(clickedImage, {
width: width,
height: height,
left: 150,
top: 150,
clipName: 'layer',
clipTo: function(ctx) {
return _.bind(clipByName, pug)(ctx)
}
});
canvas.add(pug);
};
clickedImage.src = $(laImg).attr("src");
}
And the looks like, after restriction of bounds,
Here is the fiddle I have created with some static image url.
https://jsfiddle.net/sureshatta/yxuoav39/
So I am staying with this solution for now and I really feel like this is hacky and dirty. Looking for some other clean solutions.

As far as I know you can't add a canvas to another canvas - you're getting that error as it tries to call setCoords() on the object you've added, but in this case it's another canvas and fabric.Canvas doesn't contain that method (see docs). I think a better approach would be to have two canvases and position them relatively using CSS - see this simple fiddle
HTML
<div class="parent">
<div class="artcanvas">
<canvas id="artcanvas" width="500" height="500"></canvas>
</div>
<div class="innerCanvas">
<canvas id="innerCanvas" width="200" height="200" ></canvas>
</div>
</div>
CSS
.parent {
position: relative;
background: black;
}
.artcanvas {
position: absolute;
left: 0;
top: 0;
}
.innerCanvas {
position: absolute;
left: 150px;
top: 150px;
}
JS
$(document).ready(function() {
canvas = new fabric.Canvas('artcanvas');
innerCanvas = new fabric.Canvas("innerCanvas");
var rect = new fabric.Rect({
fill: 'grey',
width: 500,
height: 500
});
canvas.add(rect);
var rect2 = new fabric.Rect({
fill: 'green',
width: 200,
height: 200
});
innerCanvas.add(rect2);
})
To handle the object serialization, you can do something like this:
var innerObjs = innerCanvas.toObject();
console.dir(innerObjs);
var outerObjs = canvas.toObject();
innerObjs.objects.forEach(function (obj) {
obj.left += leftOffset; // offset of inner canvas
obj.top += topOffset;
outerObjs.objects.push(obj);
});
var json = JSON.stringify(outerObjs);
This will then give you the JSON for all objects on both canvases

I have no understanding why you want to do this thing, but to put a canvas inside another canvas, you have one simple way:
canvas = new fabric.Canvas('artcanvas');
innerCanvas = new fabric.Canvas("innerCanvas");
imageContainer = new fabric.Image(innerCanvas.lowerCanvasEl);
canvas.add(imageContainer);
Then depending what you want to do, you may need additional tweaks, but this should work out of the box.

Don't create a canvas
Most objects in fabric (from my limited experience) are at some point converted to a canvas. Creating an additional fabric canvas to manage a group of objects is kind of pointless as you are just adding overhead and mimicking fabrics built in groups object.
Fabric objects are basically DOM canvases wrappers.
The following example shows how fabric uses a canvas to store the content of a group. The demo creates a group and adds it to the fabric canvas, then gets the groups canvas and adds it to the DOM. Clicking on the group's canvas will add a circle. Note how it grows to accommodate the new circles.
const radius = 50;
const fill = "#0F0";
var pos = 60;
const canvas = new fabric.Canvas('fCanvas');
// create a fabric group and add two circles
const group = new fabric.Group([
new fabric.Circle({radius, top : 5, fill, left : 20 }),
new fabric.Circle({radius, top : 5, fill, left : 120 })
], { left: 0, top: 0 });
// add group to the fabric canvas;
canvas.add(group);
// get the groups canvas and add it to the DOM
document.body.appendChild(group._cacheContext.canvas);
// add event listener to add circles to the group
group._cacheContext.canvas.addEventListener("click",(e)=>{
group.addWithUpdate(
new fabric.Circle({radius, top : pos, fill : "blue", left : 60 })
);
canvas.renderAll();
pos += 60;
});
canvas {
border : 2px solid black;
}
div {
margin : 10px;
}
<script src="https://cdnjs.cloudflare.com/ajax/libs/fabric.js/1.7.13/fabric.min.js"></script>
<div>Fabric's canvas "canvas = new fabric.Canvas('fCanvas');"</div>
<canvas id="fCanvas" width="256" height="140"></canvas>
<div>Fabric group canvas below. Click on it to add a circle.</div>
Use a group rather than a new instance of a fabric canvas.
As you can see a canvas is generated for you. Adding another fabric canvas (Note that a fabric canvas is not the same as a DOM canvas) will only add more work for fabric to do, which already has a lot of work to do.
You are best of to use a group and have that hold the content of the other fabric object you wish to shadow. That would also contain its content in a group.
Just an image
And just a side not, a DOM canvas is an image and can be used by fabric just as any other image. It is sometimes better to do the rendering directly to the canvas rather than via fabric so you can avoid rendering overheads that fabric needs to operate.
To add a DOM canvas to fabric just add it as an image. The border and text are not fabric object, and apart from the code to render them take up no memory, and no additional CPU overhead that would be incurred if you used a fabric canvas and objects.
const canvas = new fabric.Canvas('fCanvas');
// create a standard DOM canvas
const myImage = document.createElement("canvas");
// size it add borders and text
myImage.width = myImage.height = 256;
const ctx = myImage.getContext("2d");
ctx.fillRect(0,0,256,256);
ctx.fillStyle = "white";
ctx.fillRect(4,4,248,248);
ctx.fillStyle = "black";
ctx.font = "32px arial";
ctx.textAlign = "center";
ctx.textBaseline = "middle";
ctx.fillText("The DOM canvas!",128,128);
// use the canvas to create a fabric image and add it to fabrics canvas.
canvas.add( new fabric.Image(myImage, {
left: (400 - 256) / 2,
top: (400 - 256) / 2,
}));
canvas {
border : 2px solid black;
}
<script src="https://cdnjs.cloudflare.com/ajax/libs/fabric.js/1.7.13/fabric.min.js"></script>
<canvas id="fCanvas" width="400" height="400"></canvas>

innerCanvas.setCoords(); ìs a function, but you need it only after you set the coordinates. Or more precise, set these four elements:
innerCanvas.scaleX = 1;
innerCanvas.scaleY = 1;
innerCanvas.left = 150;
innerCanvas.top = 150;
innerCanvas.setCoords();
canvas.renderAll();

Clipping mask using fabricjs

I'm currently working on web app for photo editing using FabricJS and one of features I need to implement is something like Clipping masks from Photoshop.
For example I have this assets: frame, mask and image. I need to insert image inside frame and clip it with mask. Most tricky part is in requirements:
User should be able to modify image inside frame, e.g. move, rotate, skew... Frame itself also can be moved inside canvas.
Number of layers is not limited so user can add objects under or above masked image.
Masks, frames and images is not predefined, user should be able to upload and use new assets.
My current solution is this:
Load assets
Set globalCompositeOperation of image to source-out
Set clipTo function for image.
Add assets on canvas as a group
In this solution clipTo function preserve image inside rectangular area of frame and with help of globalCompositeOperation I'm clipping image to actual mask. At first sight it works fine but if I add new layer above this newly added group it will be cutted off because of globalCompositeOperation="source-out" rule. I've created JSFiddle to show this.
So, that else could I try? I've seen some posts on StackOverflow with advices to use SVGs for clipping mask, but if I understand it correctly SVG must contain only one path. This could be a problem because of third requirement of my app.
Any advice in right direction will help, because right now I'm totally stuck with this problem.

You can do this by using ClipPath property of Img Object which you want to mask. With this, you can Mask Any Type of Object. and also you need to add some Ctx Configuration in ClipTo function of Img Object.
check this link https://jsfiddle.net/naimsajjad/8w7hye2v/8/
(function() {
var img01URL = 'http://fabricjs.com/assets/printio.png';
var img02URL = 'http://fabricjs.com/lib/pug.jpg';
var img03URL = 'http://fabricjs.com/assets/ladybug.png';
var img03URL = 'http://fabricjs.com/assets/ladybug.png';
var canvas = new fabric.Canvas('c');
canvas.backgroundColor = "red";
canvas.setHeight(500);
canvas.setWidth(500);
canvas.setZoom(1)
var circle = new fabric.Circle({radius: 40, top: 50, left: 50, fixed: true, fill: '', stroke: '1' });
canvas.add(circle);
canvas.renderAll();
fabric.Image.fromURL(img01URL, function(oImg) {
oImg.scale(.25);
oImg.left = 10;
oImg.top = 10;
oImg.clipPath = circle;
oImg.clipTo = function(ctx) {
clipObject(this,ctx)
}
canvas.add(oImg);
canvas.renderAll();
});
var bili = new fabric.Path('M85.6,606.2c-13.2,54.5-3.9,95.7,23.3,130.7c27.2,35-3.1,55.2-25.7,66.1C60.7,814,52.2,821,50.6,836.5c-1.6,15.6,19.5,76.3,29.6,86.4c10.1,10.1,32.7,31.9,47.5,54.5c14.8,22.6,34.2,7.8,34.2,7.8c14,10.9,28,0,28,0c24.9,11.7,39.7-4.7,39.7-4.7c12.4-14.8-14-30.3-14-30.3c-16.3-28.8-28.8-5.4-33.5-11.7s-8.6-7-33.5-35.8c-24.9-28.8,39.7-19.5,62.2-24.9c22.6-5.4,65.4-34.2,65.4-34.2c0,34.2,11.7,28.8,28.8,46.7c17.1,17.9,24.9,29.6,47.5,38.9c22.6,9.3,33.5,7.8,53.7,21c20.2,13.2,62.2,10.9,62.2,10.9c18.7,6.2,36.6,0,36.6,0c45.1,0,26.5-15.6,10.1-36.6c-16.3-21-49-3.1-63.8-13.2c-14.8-10.1-51.4-25.7-70-36.6c-18.7-10.9,0-30.3,0-48.2c0-17.9,14-31.9,14-31.9h72.4c0,0,56-3.9,70.8,26.5c14.8,30.3,37.3,36.6,38.1,52.9c0.8,16.3-13.2,17.9-13.2,17.9c-31.1-8.6-31.9,41.2-31.9,41.2c38.1,50.6,112-21,112-21c85.6-7.8,79.4-133.8,79.4-133.8c17.1-12.4,44.4-45.1,62.2-74.7c17.9-29.6,68.5-52.1,113.6-30.3c45.1,21.8,52.9-14.8,52.9-14.8c15.6,2.3,20.2-17.9,20.2-17.9c20.2-22.6-15.6-28-16.3-84c-0.8-56-47.5-66.1-45.1-82.5c2.3-16.3,49.8-68.5,38.1-63.8c-10.2,4.1-53,25.3-63.7,30.7c-0.4-1.4-1.1-3.4-2.5-6.6c-6.2-14-74.7,30.3-74.7,30.3s-108.5,64.2-129.6,68.9c-21,4.7-18.7-9.3-44.3-7c-25.7,2.3-38.5,4.7-154.1-44.4c-115.6-49-326,29.8-326,29.8s-168.1-267.9-28-383.4C265.8,13,78.4-83.3,32.9,168.8C-12.6,420.9,98.9,551.7,85.6,606.2z',{top: 0, left: 180, fixed: true, fill: 'white', stroke: '', scaleX: 0.2, scaleY: 0.2 });
canvas.add(bili);
canvas.renderAll();
fabric.Image.fromURL(img02URL, function(oImg) {
oImg.scale(0.5);
oImg.left = 180;
oImg.top = 0;
oImg.clipPath = bili;
oImg.clipTo = function(ctx) {
clipObject(this,ctx)
}
canvas.add(oImg);
canvas.renderAll();
});
function clipObject(thisObj,ctx)
{
if (thisObj.clipPath) {
ctx.save();
if (thisObj.clipPath.fixed) {
var retina = thisObj.canvas.getRetinaScaling();
ctx.setTransform(retina, 0, 0, retina, 0, 0);
// to handle zoom
ctx.transform.apply(ctx, thisObj.canvas.viewportTransform);
thisObj.clipPath.transform(ctx);
}
thisObj.clipPath._render(ctx);
ctx.restore();
ctx.clip();
var x = -thisObj.width / 2, y = -thisObj.height / 2, elementToDraw;
if (thisObj.isMoving === false && thisObj.resizeFilter && thisObj._needsResize()) {
thisObj._lastScaleX = thisObj.scaleX;
thisObj._lastScaleY = thisObj.scaleY;
thisObj.applyResizeFilters();
}
elementToDraw = thisObj._element;
elementToDraw && ctx.drawImage(elementToDraw,
0, 0, thisObj.width, thisObj.height,
x, y, thisObj.width, thisObj.height);
thisObj._stroke(ctx);
thisObj._renderStroke(ctx);
}
}
})();
<script src="https://cdnjs.cloudflare.com/ajax/libs/fabric.js/3.6.3/fabric.min.js"></script>
<canvas id="c" width="400" height="400"></canvas>

Not sure what you want.
If you want the last image loaded (named img2), the one you send to the back to not effect the layers above do the following.
You have mask,frame,img, and img2;
Put them in the following order and with the following comp settings.
img2, source-over
img, source-over
mask, destination-out
frame, source-over
If you want something else you will have to explain it in more detail.
Personally when I provide masking to the client I give them full access to all the composite methods and allow them to work out what they need to do to achieve a desired effect. Providing a UI that allows you to change the comp setting, and layer order makes it a lot easier to sort out the sometimes confusing canvas composite rules.

I'd suggest looking at this solution.
Multiple clipping areas on Fabric.js canvas
You end up with a shape layer that is used to define the mask shape. That shape then gets applied as a clipTo to your image.
The one limitation I can think off though that you might run into is when you start to rotate various shapes. I know I have it working great with a rectangle and a circle, however ran into some issues with polygons from what I recall... This was all setup under and older version of FabricJS however, so there may have been some improvements there that I'm not experienced with.
The other issue I ran into was drop shadows didn't render correctly when passed to a NodeJS server running FabricJS.

Diagram creater using KineticJS

I'm working on a simple diagram editor using KineticJS. I would like to use two separate canvases for the palette area (that contains a number of Kinetic.Groups that represent the different nodes of the network I might create), and the diagramming area where I can add nodes from the palette via drag and drop, and then add connections between the various nodes as specific anchor points. I'm having trouble figuring out the drag and drop process from the palette canvas of (stationary) Kinetic.Groups over to the other canvas containing diagramming area. I'm guessing that I need to fire off of the dragstart event for the palette objects (although I don't want these themselves to be draggable), and then do something like create an opague copy of the palette object that can be dragged around, and finally dropped into the diagramming area (with full opacity).
Can groups be dragged outside of a the staging canvases boundaries? Maybe I need to generate an image when I start to drag from the palette, drag that image over, and then create another group when dropping into the diagramming area.
Does any one know of any examples that might point me in the right direction, or who can offer some insight (even code) into the required process. I've searched the KineticJS examples but can't quite find enough to get me going.

Here’s one way to drag nodes from a source palette into a destination group:
A Fiddle: http://jsfiddle.net/m1erickson/xtVyL/
Network nodes are represented by small icons (which are really small kinetic image objects).
The user can drag any icon from the source palette to any destination group.
The groups are just defined areas on the canvas, but could be Kinetc.Groups for more flexibility.
During the dragend event, a new duplicate copy of the dragged icon is created in the destination group.
After the dragend event is complete, the original palette icon is automatically moved from
The newly created duplicate icon can be dragged around the destination group (but not outside that group).
Here is code and a Fiddle: http://jsfiddle.net/m1erickson/xtVyL/
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>Prototype</title>
<script type="text/javascript" src="http://code.jquery.com/jquery.min.js"></script>
<script src="http://d3lp1msu2r81bx.cloudfront.net/kjs/js/lib/kinetic-v4.5.5.min.js"></script>
<style>
#container{
border:solid 1px #ccc;
margin-top: 10px;
width:350px;
height:350px;
}
</style>
<script>
$(function(){
var stage = new Kinetic.Stage({
container: 'container',
width: 350,
height: 350
});
var layer = new Kinetic.Layer();
stage.add(layer);
// image loader
var imageURLs=[];
var imagesOK=0;
var imgs=[];
imageURLs.push("https://dl.dropboxusercontent.com/u/139992952/stackoverflow/tempPC.png");
imageURLs.push("https://dl.dropboxusercontent.com/u/139992952/stackoverflow/tempServer.png");
imageURLs.push("https://dl.dropboxusercontent.com/u/139992952/stackoverflow/tempRouter.png");
loadAllImages();
function loadAllImages(callback){
for (var i = 0; i < imageURLs.length; i++) {
var img = new Image();
imgs.push(img);
img.onload = function(){
imagesOK++;
if (imagesOK==imageURLs.length ) {
start();
}
};
img.src = imageURLs[i];
}
}
// top icon positions
var nextIconX=20;
var nextIconY=20;
// define groups
var groups=[];
groups.push({x:0,y:100,w:175,h:250,fill:"skyblue"});
groups.push({x:175,y:100,w:175,h:250,fill:"cornsilk"});
// add boundary info to each group
// draw colored rect to show group area
for(var i=0;i<groups.length;i++){
var g=groups[i];
g.left=g.x;
g.right=g.x+g.w;
g.top=g.y;
g.bottom=g.y+g.h;
var rect=new Kinetic.Rect({
x:g.x,
y:g.y,
width:g.w,
height:g.h,
fill:g.fill,
stroke:"gray"
});
layer.add(rect);
}
// hittest for each group
function groupHit(x,y){
for(var i=0;i<groups.length;i++){
var g=groups[i];
if(x>g.left && x<g.right && y>g.top && y<g.bottom){return(i);}
}
return(-1);
}
function start(){
makePaletteIcon(imgs[0]);
makePaletteIcon(imgs[1]);
makePaletteIcon(imgs[2]);
layer.draw();
}
function makePaletteIcon(img){
// make an icon that stays in the pallette tray
var fixedIcon=newImage(nextIconX,nextIconY,img,false);
layer.add(fixedIcon);
// make an icon that is dragged from the tray to a group
var dragIcon=makeDraggableIcon(nextIconX,nextIconY,img);
layer.add(dragIcon);
// calc the next icon position
nextIconX+=(img.width+20);
}
function makeDraggableIcon(x,y,img){
var i=newImage(x,y,img,true);
//
i.trayX=x;
i.trayY=y;
//
i.setOpacity(0.50);
i.on("dragend",function(){
var x=this.getX();
var y=this.getY();
// if this pallette icon was not dropped in a group
// put the icon back in the tray and return
var hit=groupHit(x,y);
if(hit==-1){
this.setPosition(this.trayX,this.trayY);
return;
}
// add a copy of this icon to the drop group
var component=newImage(x,y,this.getImage(),true);
// set drag limits
var group=groups[hit];
component.maxDragLeft=group.left;
component.maxDragRight=group.right;
component.maxDragTop=group.top;
component.maxDragBottom=group.bottom;
// limit component dragging to inside the assigned group
component.setDragBoundFunc(function(pos) {
var xx=pos.x;
var yy=pos.y;
var w=this.getWidth();
var h=this.getHeight();
if(pos.x<this.maxDragLeft){xx=this.maxDragLeft;}
if(pos.x+w>this.maxDragRight){xx=this.maxDragRight-w;}
if(pos.y<this.maxDragTop){yy=this.maxDragTop;}
if(pos.y+h>this.maxDragBottom){yy=this.maxDragBottom-h;}
return{ x:xx, y:yy };
});
layer.add(component);
// move the dragIcon back into the pallette tray
this.setPosition(this.trayX,this.trayY);
layer.draw();
});
return(i);
}
// make a new Kinetic.Image
function newImage(x,y,img,isDraggable){
var i=new Kinetic.Image({
image:img,
x: x,
y: y,
width: img.width,
height: img.height,
draggable:isDraggable
});
return(i);
}
}); // end $(function(){});
</script>
</head>
<body>
<p>Drag any icon from top into blue or yellow group</p>
<div id="container"></div>
</body>
</html>

How to save/export a DOM element to an image?

I have a web page which has a form element (with its ID known) and
inside the form there are multiple DIVs, and the position of each div
may be changed.
What I'd like to do is:
a) Save the current state of this form
// var currentForm=document.forms['myFrm'].innerHTML;
would probably suffice...
b) Save or export the entire form with the most current position of each DIV
to an image file.
// how to save/export the javascript var of currentForm to an image
file is the key question.
Any help/pointer would be appreciated.

After hours of research, I finally found a solution to take a screenshot of an element, even if the origin-clean FLAG is set (to prevent XSS), that´s why you can even capture for example Google Maps (in my case). I wrote an universal function to get a screenshot. The only thing you need in addition is the html2canvas library (https://html2canvas.hertzen.com/).
Example:
getScreenshotOfElement($("div#toBeCaptured").get(0), 0, 0, 100, 100, function(data) {
// in the data variable there is the base64 image
// exmaple for displaying the image in an <img>
$("img#captured").attr("src", "data:image/png;base64,"+data);
}
Keep in mind console.log() and alert() won´t generate an output if the size of the image is great.
Function:
function getScreenshotOfElement(element, posX, posY, width, height, callback) {
html2canvas(element, {
onrendered: function (canvas) {
var context = canvas.getContext('2d');
var imageData = context.getImageData(posX, posY, width, height).data;
var outputCanvas = document.createElement('canvas');
var outputContext = outputCanvas.getContext('2d');
outputCanvas.width = width;
outputCanvas.height = height;
var idata = outputContext.createImageData(width, height);
idata.data.set(imageData);
outputContext.putImageData(idata, 0, 0);
callback(outputCanvas.toDataURL().replace("data:image/png;base64,", ""));
},
width: width,
height: height,
useCORS: true,
taintTest: false,
allowTaint: false
});
}

There is a library called Domvas that should do what you want.
It gives you the ability to take arbitrary DOM content and paint it to
a Canvas of your choice.
After that exporting an image from a canvas element should be pretty easy:
var canvas = document.getElementById("mycanvas");
var img = canvas.toDataURL("image/png");
document.write('<img src="'+img+'"/>');

Do you want to do it completely in JavaScript? If so, one possible solution could be to transform the HTML to an SVG. Or maybe you can use the <canvas> tag and draw it manually.