Just a spinnin' my wheels on this one. I'm trying to get a start into the node.js/fabric/express world and can't seem to get past this wall of "Could not initialize canvas element".
I've created a new express.js application using the generator:
https://expressjs.com/en/starter/generator.html
Here's a simple working example of what I'm trying to accomplish within my express application framework:
https://jsfiddle.net/6dcgakb6/
I haven't touched most of the auto generated files, except to add jquery and a public/javascripts/myApp.js file for client side javascript. It's within this file I think I'm having the issues or I'm not understanding basic principles.
I'm including scripts jquery.js, fabric.js, and myApp.js in <head> of my HTML layout in that order. I added routes to routes/index.js so that I can include them using <script src="fabric/fabric.js">.
router.get('/jquery/jquery.js', function(req, res, next) {
res.sendFile(path.resolve(appDir + '/../node_modules/jquery/dist/jquery.min.js'));
});
router.get('/fabric/fabric.js', function(req, res, next) {
res.sendFile(path.resolve(appDir + '/../node_modules/fabric/dist/fabric.js'));
});
The body simply contains a <canvas id="c"></canvas> element.
Then, in myApp.js:
$(document).ready(function(){
var canvas = new fabric.Canvas('c');
var rect = new fabric.Rect({
left: 100,
top: 100,
fill: 'red',
width: 20,
height: 20,
angle: 45
});
canvas.add(rect);
});
When visiting the page, I receive the error message:
jquery.js:2 Uncaught Error: Could not initialize `canvas` element
(anonymous function) # fabric.js:5989
(anonymous function) # fabric.js:7633
After playing around for a bit, I did find that I can run var canvasEl = fabric.document.createElement('canvas') without any error. I can also run var canvas = new fabric.Canvas(); without error as well (notice the missing constructor parameter value of 'c').
I would really appreciated some help on this one. Again, I wonder if I'm missing a key design principle for including and initializing client side javascript using the express framework or if I'm missing something else terrible simple.
I've searched for a solution, but have been unsuccessful in doing so. Here are some interesting links I found along the way in case they are helpful to others.
https://github.com/kangax/fabric.js/issues/573
https://groups.google.com/forum/#!topic/fabricjs/Qix_Z-2AJ2o
Facepalm
Okay, it was a type-o. I wrote <cavnas id="c"> instead of <canvas id="c">.
Related
The use case I'm trying to fulfill:
Admin adds SVG along with new content in CMS, specifying in the CMS which svg goes with which content
CMS commits change to git (Netlify CMS)
Static site builds again
SVG is added inline so that it can be styled and/or animated according to the component in which it occurs
Now - I can't figure out a clean way to add the SVG inline. My logic tells me - everything is available at build time (the svgs are in repo), so I should be able to simply inline the svgs. But I don't know how to generically tell React about an svg based on variables coming from the CMS content. I can import the svg directly using svgr/weback, but then I need to know the file name while coding, which I don't since it's coming from the CMS. I can load the svg using fs.readFileSync, but then the SVG gets lost when react executes client-side.
I added my current solution as an answer, but it's very hacky. Please tell me there's a better way to do this with react!
Here is my current solution, but it's randomly buggy in dev mode and doesn't seem to play well with next.js <Link /> prefetching (I still need to debug this):
I. Server-Side Rendering
Read SVG file path from CMS data (Markdown files)
Load SVG using fs.readFileSync()
Sanitize and add the SVG in React
II. Client-Side Rendering
Initial Get:/URL response contains the SVGs (ssr worked as intended)
Read the SVGs out of the DOM using HTMLElement.outerHTML
When React wants to render the SVG which it doesn't have, pass it the SVG from the DOM
Here is the code.
import reactParse from "html-react-parser";
import DOMPurify from "isomorphic-dompurify";
import * as fs from "fs";
const svgs = {}; // { urlPath: svgCode }
const createServerSide = (urlPath) => {
let path = "./public" + urlPath;
let svgCode = DOMPurify.sanitize(fs.readFileSync(path));
// add id to find the SVG client-side
// the Unique identifier is the filepath for the svg in the git repository
svgCode = svgCode.replace("<svg", `<svg id="${urlPath}"`);
svgs[urlPath] = svgCode;
};
const readClientSide = (urlPath) => {
let svgElement = document.getElementById(urlPath);
let svgCode = svgElement.outerHTML;
svgs[urlPath] = svgCode;
};
const registerSVG = (urlPath) => {
if (typeof window === "undefined") {
createServerSide(urlPath);
} else {
readClientSide(urlPath);
}
return true;
};
const inlineSVGFromCMS = (urlPath) => {
if (!svgs[urlPath]) {
registerSVG(urlPath);
}
return reactParse(svgs[urlPath]);
};
export default inlineSVGFromCMS;
We are a team of 5 developers working on a video rendering implementation. This implementation consists out of two parts.
A live video preview in the browser using angular + konva.
A node.js (node 14) serverless (AWS lambda container) implementation using konva-node that pipes frames to ffmpeg for rendering a mp4 video in higher quality for later download.
Both ways are working for us. Now we extracted the parts of the animation that are the same for frontend and backend implementation to an internal library. We imported them in BE and FE. That also works nicely for most parts.
We noticed here that konva-node is deprecated since a short time. Documentation says to use canvas + konva instead on node.js. But this just doesn't work. If we don't use konva-node we cannot create a stage without a 'container' value. Also we cannot create a raw image buffer anymore, because stage.toCanvas() actually returns a HTMLCanvas, which does not have this functionality.
So what does konva-node actually do to konva API?
Is node.js still supported after deprecation of konva-node?
How can we get toBuffer() and new Stage() functionality without konva-node in node.js?
backend (konva-node)
import konvaNode = require('konva-node');
this.stage = new konvaNode.Stage({
width: stageSize.width,
height: stageSize.height
});
// [draw stuff on stage here]
// create raw frames to pipe to ffmpeg
const frame = await this.stage.toCanvas();
const buffer: Buffer = frame.toBuffer('raw');
frontend (konva)
import Konva from 'konva';
this.stage = new Konva.Stage({
width: stageSize.width,
height: stageSize.height,
// connect stage to html element in browser
container: 'container'
});
// [draw stuff on stage here]
Finally in an ideal world (if we could just Konva in frontend and backend without konva-node the following should be possible for a shared code.
loading images
public static loadKonvaImage(element, canvas): Promise<any> {
return new Promise(resolve => {
let image;
if (canvas) {
// node.js canvas image
image = new canvas.Image();
} else {
// html browser image
image = new Image();
}
image.src = element.url;
image.onload = function () {
const konvaImage = new Konva.Image(
{image, element.width, element.height});
konvaImage.cache();
resolve(konvaImage);
};
});
}
Many props to the developer for the good work. We would look forward to use the library for a long time, but how can we if some core functionality that we rely on is outdated shortly after we started the project?
Another stack overflow answer mentioned Konva.isBrowser = false;. Maybe this is used to differentiate between a browser and a node canvas?
So what does konva-node actually do to konva API?
It slightly patches Konva code to use canvas nodejs library to use 2d canvas API. So, Konva will not use browser DOM API.
Is node.js still supported after deprecation of konva-node?
Yes. https://github.com/konvajs/konva#4-nodejs-env
How can we get toBuffer() and new Stage() functionality without konva-node in node.js?
You can try to use this:
const canvas = layer.getNativeCanvasElement();
const buffer = canvas.toBuffer();
We have solved the problems we had the following way:
create stage (shared between Be+FE)
public static createStage(stageWidth: number, stageHeight: number, canvas?: any): Konva.Stage {
const stage = new Konva.Stage({
width: stageWidth,
height: stageHeight,
container: canvas ? canvas : 'container'
});
return stage;
}
create raw image buffer (BE)
const frame: any = await this.stage.toCanvas();
const buffer: Buffer = frame.toBuffer('raw');
loading images (shared between Be+FE)
public static loadKonvaImage(element, canvas?: any): Promise<Konva.Image> {
return new Promise(resolve => {
const image = canvas ? new canvas.Image() : new Image();
image.src = element.url;
image.onload = function () {
const konvaImage = new Konva.Image(
{image, element.width, element.height});
konvaImage.cache();
resolve(konvaImage);
};
});
}
Two things we had to do.
We have rewritten our whole backend and library code to use ESM modules and we got rid of konva-node and konva 7 in general.
We defined the node module canvas in all places as any. It seems like Konva accepts more inputs than expected and like specified in the type interfaces of the classes. canvas is only installed in the backend and inserted in some library methods like shown above.
#lavrton nice to hear from you. Your answer might also work for getting the Buffer, but you didn't answer on how to create the stage. Luckily we found a solution for both issues.
I have an Electron app that loads URL from PHP server. And the page contains an iFrame having a source to PDF. The PDF page seems absolutely ok in a normal web browser but asks for download in Electron. Any help?
My codes for html page is
<h1>Hello World!</h1>
Some html content here...
<iframe src="http://mozilla.github.io/pdf.js/web/compressed.tracemonkey-pldi-09.pdf" width="1200" height="800"></iframe>
And my js code is something like
mainWindow = new BrowserWindow({width: 800, height: 600})
mainWindow.loadURL(url.format({
pathname: path.join(__dirname, 'index.html'),
protocol: 'file:',
slashes: true
}))
app.on('ready', createWindow)
Any help would be really greatful...
Electron is shipping already with an integrated PDF viewer.
So you can load PDF files just like normal HTML files, the PDF viewer will automatically show up.
E.g. in BrowserWindow with .loadURL(…), in <iframes>, <object> and also with the, at the moment discouraged, <webview>.
PS: The need to enable the plugins property in the BrowserWindow or <webview> is no more needed since Electron 9.
You will need
https://github.com/gerhardberger/electron-pdf-window
Example:
const { app } = require('electron')
const PDFWindow = require('electron-pdf-window')
app.on('ready', () => {
const win = new PDFWindow({
width: 800,
height: 600
})
win.loadURL('http://mozilla.github.io/pdf.js/web/compressed.tracemonkey-pldi-09.pdf')
})
This answer will focus on implementation with Angular.
After year of waiting (to be solved by the Electron) finally I decided to apply a workaround. For the people who needs it done, here it goes. Workaround comes with a cost of increasing bundle size totally 500K. (For Angular)
Workaround to use Mozilla PDF.js library.
NPM
GitHub
Implementation 1 (Setting nodeIntegration: true)
This implementation has no issue, you can implement by the document of the library mentioned. But if you run into additional problem like creating white window when route is changed, it is due to the setting nodeIntegration property to true. If so, use the following implementation.
Implementation 2 (Setting nodeIntegration: false)
This is the default by Electron. Using this configuration and viewing the PDF is bit tricky. Solution is to use Uint8Array instead of a blob or base64.
You can use the following function to convert base64 to Uint8Array.
base64ToArrayBuffer(data): Uint8Array {
const input = data.substring(data.indexOf(',') + 1);
const binaryString = window.atob(input ? input : data);
const binaryLen = binaryString.length;
const bytes = new Uint8Array(binaryLen);
for (let i = 0; i < binaryLen; i++) {
const ascii = binaryString.charCodeAt(i);
bytes[i] = ascii;
}
return bytes;
}
Or convert blob to array buffer
const blob = response;
let arrayBuffer = null;
arrayBuffer = await new Response(blob).arrayBuffer();
then pass the generated Uint8Array as the pdfSource to the ng2-pdfjs-viewer.
HTML
<ng2-pdfjs-viewer zoom="100" [pdfSrc]="pdfSource"></ng2-pdfjs-viewer>
Electron 9.0.0 has enabled PDF viewer already.
npm install electron#9.0.0
Has anyone worked on a real time project with fabric.js/socket.io?
My canvas works fine but somewhere along, the canvas just turns white for one user (the other user's canvas appears normal). The objects are still on the canvas but they are white. Then after a minute the canvas's objects turn back to their original color.
I am simply serializing the canvas sending it to the server and broadcasting the canvas to all clients(except user). Canvas is then cleared, de-serialized and loaded on to the canvas.
How do I achieve a smooth real time canvas between 2 clients without any of these unexpected canvas glitches! I'm not sure if I am using socket.io or fabric.js wrong. Please advice me!
//client side code
var socket = io();
socket.on('canvas', function(canvasobj){
canvas.clear();
canvas.loadFromJSON(canvasobj, canvas.renderAll.bind(canvas));
});
canvas.on('mouse:up', function(options){
var canvasStr = JSON.stringify(canvas);
socket.emit('canvas', canvasStr);
});
//node.js code
io.on('connection', function(socket){
socket.on('canvas', function(canvasobj){
socket.broadcast.emit('canvas', canvasobj);
});
});
I am not really sure, but try
canvas.on('mouse:up', function(event){
event.preventDefault();
var canvasStr = JSON.stringify(canvas);
socket.emit('canvas', canvasStr);
});
I've been trying to figure out how to render react on the server (node/express) and finally found a simple enough tutorial to understand what's going on. But now, after setting everything up, I'm getting an error in the React.render method:
here's my component file:
var React = require('react');
var box = React.createClass({
render: function() {
return (
<div style='padding: 10px'>
this.props.text
</div>
);
}
});
React.render(<box text='testing server side'/>, document.body);
module.exports = box;
I get an error when I run npm start:
document is not defined
how do I get around this? do I need or not need the render method?
to give more context, this box component is being required by another component:
var React = require('react');
var Box = require('../react-jsx/box.js'); //this is the box component
var Component = React.createClass({
render: function() {
return (
<html>
<head>
<title>
React Server Rendering
</title>
</head>
<body>
<Box text='testing'/>
<script src="public/bundle.js"></script>
</body>
</html>
);
}
});
module.exports = Component;
and this is all being used in index.js
require('node-jsx').install();
var React = require('react');
var Component = require('../custom-modules/test-react-server-module.js');
var express = require('express');
var router = express.Router();
router.get('/react', function(req, res, next) {
var markup = React.renderToString(Component());
res.send(markup);
});
module.exports = router;
and if I remove the render method I get this error in the browser:
Cannot read property '__reactAutoBindMap' of undefined
I saw some people saying that may be due to the jsx transformer being old, but I think I have the latest version
I'm out of ideas
First of all, I'd recommend update your React version. The current version exposes two different Top-Level API's: React, which is generally used to create components and ReactDOM, which exposes DOM-specific methods to be used at the top level of your app.
There is to things to point out here:
You are trying to run an code that is supposed to be executed only at the browser. There is no document in NodeJS. I'd suggest using webpack to pack this component files and serve them on browser.
For an isomorphic React application, you need to have a client.js file that calls the render function for the same component you are trying to render inside index.js. Got it?
Understand the ReactDOM.render, as the documentation states:
Render a ReactElement into the DOM in the supplied container and return a reference to the component (or returns null for stateless components).
If the ReactElement was previously rendered into container, this will
perform an update on it and only mutate the DOM as necessary to
reflect the latest React component.
Keep in mind, again, that ReactDOM.render should be only used a few times and generally at the top level of your app, just one time.
Having said this, your box.js should look like:
var React = require('react');
var box = React.createClass({
render: function() {
return (
<div style='padding: 10px'>
this.props.text
</div>
);
}
});
module.exports = box;
For this to properly work, you will need to create a main component main-component-file.js:
var React = require('react');
var Box = require('../react-jsx/box.js'); //this is the box component
var Component = React.createClass({
render: function() {
return (
<html>
<head>
<title>
React Server Rendering
</title>
</head>
<body>
<Box text='testing'/>
<script src="public/bundle.js"></script>
</body>
</html>
);
}
});
module.exports = Component;
Inside your bundle.js you need to make sure that this is being called so the main component tries to re-render:
var React = require('react');
var ReactDOM = require('react-dom');
var Component = require('main-component-file.js');
ReactDOM.render(<Component/>, document.body);
At last but not least: index.js, the server file. Change React.renderToString to ReactDOMServer.renderToString, create a React Element from your main component and use it:
var element = React.createElement(Component)
router.get('/react', function(req, res, next) {
var markup = ReactDOMServer.renderToString(element);
res.send(markup);
});
Don't forget to include the npm package react-dom/server at your index.js.
References used in the article:
React.createElement
ReactDOM.render() docs
ReactDOMServer docs
You should delete this
React.render(<box text='testing server side'/>, document.body);
There is no need for it. What you are essentially telling React to do is render it right then and there.
document.body doesn't exist yet because you are rendering it server-side and you also don't need it because you render the component in the renderToString function upon request in the router. (Also I think #PeterLyons is correct so take a look at his answer too).
Also if you are strictly using React for views only, you might want to take a look at express-react-views. They have a good tutorial of how to use React with Express and you essentially can use it for server-side rendering only. I don't think it's as ideal as using react-router depending on what you're building but it illustrates how React is handling the server-side rendering and works with Express.
You need to use the react-dom/server package's renderToString function in the server environment. This will return the HTML as a string which you can send in your express response.