React Component to Draw using Hooks and Typescript

Recently, How to Create the Drawing Interaction on DEV's Offline Page by Ali Spittel showed up in my feed and it looked quite cool. This got me wondering if I could create the same thing as a React component using Hooks and typescript. Well, the fact that I am writing this post means I was able to recreate it. So let's see how I did it.

If you are interested in the final product, you can check out the Github repository. There is also a sandbox you can play with at the end of this post.

This post assumes you already know how to work with TypeScript and hooks.

Creating the Component

The first thing we need to do is to create a Canvas component. The canvas needs to take up some space which we will want any parent component to be able to override so we will add width and height as props. But, We want to add a sensible default so that We don't have to add these props every time we want to use this component. We will add some defaultProps to set these values to window.innerWidth and window.innerHeight respectively.

import React from 'react';

interface CanvasProps {
width: number;
height: number;
}

const Canvas = ({ width, height }: CanvasProps) => {
return <canvas height={height} width={width} />;
};

Canvas.defaultProps = {
width: window.innerWidth,
height: window.innerHeight,
};

export default Canvas;

Lets Draw

Since we need to modify the canvas element, we will need to add a ref to it. We can do this by using useRef hook and modifying our canvas element to set the ref.

const canvasRef = useRef<HTMLCanvasElement>(null);
return <canvas ref={canvasRef} height={height} width={width} />;

Set state

We need to keep track of some variables

  • the mouse position.
  • whether we are painting or not.

We can do this by adding the useState hook. 

We will also create a Coordinate type to help with keeping track of mouse positions.

type Coordinate = {
x: number;
y: number;
};

const Canvas = ({ width, height }: CanvasProps) => {
const [isPainting, setIsPainting] = useState(false);
const [mousePosition, setMousePosition] = useState<Coordinate | undefined>(undefined);
// … other stuff here

Start drawing when the mouse is pressed.

We will add the event listener in the useEffect hook. If we have a valid reference to the canvas, we add an event listener to the mouseDown event. We also remove the event listener when we unmount.

 useEffect(() => {
if (!canvasRef.current) {
return;
}
const canvas: HTMLCanvasElement = canvasRef.current;
canvas.addEventListener(‘mousedown’, startPaint);
return () => {
canvas.removeEventListener(‘mousedown’, startPaint);
};
}, [startPaint]);

startPaint needs to get the current coordinates of the mouse and set isPainting to true. We will also wrap it in a useCallback hook so that we can use it inside the useEffect hook.

 const startPaint = useCallback((event: MouseEvent) => {
const coordinates = getCoordinates(event);
if (coordinates) {
setIsPainting(true);
setMousePosition(coordinates);
}
}, []);

// …other stuff here

const getCoordinates = (event: MouseEvent): Coordinate | undefined => {
if (!canvasRef.current) {
return;
}

const canvas: HTMLCanvasElement = canvasRef.current;
return [event.pageX - canvas.offsetLeft, event.pageY - canvas.offsetTop];

};

Draw the line on mouse move

Similar to the mouseDown event listener we will use the useEffect hook to add the mousemove event.

useEffect(() => {
if (!canvasRef.current) {
return;
}
const canvas: HTMLCanvasElement = canvasRef.current;
canvas.addEventListener(‘mousemove’, paint);
return () => {
canvas.removeEventListener(‘mousemove’, paint);
};
}, [paint]);

paint needs to

  • Check if we are painting.
  • Get the new mouse coordinates.
  • Draw a line from the old coordinates to the new one by getting the rendering context from the canvas.
  • Update the old coordinates.
const paint = useCallback(
(event: MouseEvent) => {
if (isPainting) {
const newMousePosition = getCoordinates(event);
if (mousePosition && newMousePosition) {
drawLine(mousePosition, newMousePosition);
setMousePosition(newMousePosition);
}
}
},
[isPainting, mousePosition]
);

// …other stuff here

const drawLine = (originalMousePosition: Coordinate, newMousePosition: Coordinate) => {
if (!canvasRef.current) {
return;
}
const canvas: HTMLCanvasElement = canvasRef.current;
const context = canvas.getContext(‘2d’);
if (context) {
context.strokeStyle = ‘red’;
context.lineJoin = ‘round’;
context.lineWidth = 5;

        context.beginPath();
        context.moveTo(originalMousePosition.x, originalMousePosition.y);
        context.lineTo(newMousePosition.x, newMousePosition.y);
        context.closePath();

        context.stroke();
    }
};

Stop drawing on mouse release

We want to stop drawing when either the user releases the mouse or they move the mouse out of the canvas area

useEffect(() => {
if (!canvasRef.current) {
return;
}
const canvas: HTMLCanvasElement = canvasRef.current;
canvas.addEventListener(‘mouseup’, exitPaint);
canvas.addEventListener(‘mouseleave’, exitPaint);
return () => {
canvas.removeEventListener(‘mouseup’, exitPaint);
canvas.removeEventListener(‘mouseleave’, exitPaint);
};
}, [exitPaint]);

In exitPaint we just set the isPainting to false

const exitPaint = useCallback(() => {
setIsPainting(false);
}, []);

And, we have a React component that we can reuse. You can see the final code in either the Github repository. Play with the sandbox below.

Sandbox


Let me if you have any questions in the comments, thanks for reading!

#typescript #reactjs #react-native #web-development

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React Component to Draw using Hooks and Typescript
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In the article, we discuss the similarities between native mobile development and development using React Native. We also touch upon where they differ and how to bridge the gaps. Read on.

A brief introduction to React Native

Let’s briefly set the context first. We will briefly touch upon what React Native is and how it differs from earlier hybrid frameworks.

React Native is a popular JavaScript framework that Facebook has created. You can use this open-source framework to code natively rendering Android and iOS mobile apps. You can use it to develop web apps too.

Facebook has developed React Native based on React, its JavaScript library. The first release of React Native came in March 2015. At the time of writing this article, the latest stable release of React Native is 0.62.0, and it was released in March 2020.

Although relatively new, React Native has acquired a high degree of popularity. The “Stack Overflow Developer Survey 2019” report identifies it as the 8th most loved framework. Facebook, Walmart, and Bloomberg are some of the top companies that use React Native.

The popularity of React Native comes from its advantages. Some of its advantages are as follows:

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  • 3rd party plugins: This framework supports 3rd party plugins.
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Why React Native is fundamentally different from earlier hybrid frameworks

Are you wondering whether React Native is just another of those hybrid frameworks like Ionic or Cordova? It’s not! React Native is fundamentally different from these earlier hybrid frameworks.

React Native is very close to native. Consider the following aspects as described on the React Native website:

  • Access to many native platforms features: The primitives of React Native render to native platform UI. This means that your React Native app will use many native platform APIs as native apps would do.
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Due to these factors, React Native offers many more advantages compared to those earlier hybrid frameworks. We now review them.

#android app #frontend #ios app #mobile app development #benefits of react native #is react native good for mobile app development #native vs #pros and cons of react native #react mobile development #react native development #react native experience #react native framework #react native ios vs android #react native pros and cons #react native vs android #react native vs native #react native vs native performance #react vs native #why react native #why use react native

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Here are the steps I followed to change my class component to a functional component:

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Required Fields

The most simple, yet very common, validation is to make sure that an input component contains input from the user. React Hook Form basic concept is to register input tags to the form by passing register() to the tag’s ref attribute. As we can see here:

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Follow these step-by-step instructions to create an animated accordion component in React.js using React Hooks and CSS.

🗂 DOWNLOADS 🗂

https://gum.co/AEeem

🔗 HELPFUL RESOURCES 🔗

React DOM Elements: https://reactjs.org/docs/dom-elements.html

Overview of dangerouslySetInnerHTML: https://react-cn.github.io/react/tips/dangerously-set-inner-html.html

How to prevent XSS attacks when using dangerouslySetInnerHTML in React: https://dev.to/jam3/how-to-prevent-xss-attacks-when-using-dangerouslysetinnerhtml-in-react-1464

Hooks API Reference: https://reactjs.org/docs/hooks-reference.html

Visual Studio Code: https://code.visualstudio.com/

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