react-signature-canvas

A React wrapper component around signature_pad.

Originally, this was just an unopinionated fork of react-signature-pad that did not impose any styling or wrap any other unwanted elements around your canvas -- it's just a wrapper around a single canvas element! Hence the naming difference. Nowadays, this repo / library has significantly evolved, introducing new features, fixing various bugs, and now wrapping the upstream signature_pad to have its updates and bugfixes baked in.

This fork also allows you to directly pass props to the underlying canvas element, has new, documented API methods you can use, has new, documented props you can pass to it, has a live demo, has a CodeSandbox playground, has 100% test coverage, and is written in TypeScript.

Installation

npm i -S react-signature-canvas

Usage

import React from 'react'
import { createRoot } from 'react-dom/client'
import SignatureCanvas from 'react-signature-canvas'

createRoot(
  document.getElementById('my-react-container')
).render(
  <SignatureCanvas penColor='green'
    canvasProps={{width: 500, height: 200, className: 'sigCanvas'}} />,
)

Props

The props of SignatureCanvas mainly control the properties of the pen stroke used in drawing. All props are optional.

• velocityFilterWeight : number, default: 0.7
• minWidth : number, default: 0.5
• maxWidth : number, default: 2.5
• minDistance: number, default: 5
• dotSize : number or function, default: () => (this.minWidth + this.maxWidth) / 2
• penColor : string, default: 'black'
• throttle: number, default: 16

There are also two callbacks that will be called when a stroke ends and one begins, respectively.

• onEnd : function
• onBegin : function

Additional props are used to control the canvas element.

• canvasProps: object
  • directly passed to the underlying <canvas /> element
• backgroundColor : string, default: 'rgba(0,0,0,0)'
  • used in the API's clear convenience method (which itself is called internally during resizes)
• clearOnResize: bool, default: true
  • whether or not the canvas should be cleared when the window resizes

Of these props, all, except for canvasProps and clearOnResize, are passed through to signature_pad as its options. signature_pad's internal state is automatically kept in sync with prop updates for you (via a componentDidUpdate hook).

API

All API methods require a ref to the SignatureCanvas in order to use and are instance methods of the ref.

import React, { useRef } from 'react'
import SignatureCanvas from 'react-signature-canvas'

function MyApp() {
  const sigCanvas = useRef(null);

  return <SignatureCanvas ref={sigCanvas} />
}

• isEmpty() : boolean, self-explanatory
• clear() : void, clears the canvas using the backgroundColor prop
• fromDataURL(base64String, options) : void, writes a base64 image to canvas
• toDataURL(mimetype, encoderOptions): base64string, returns the signature image as a data URL
• fromData(pointGroupArray): void, draws signature image from an array of point groups
• toData(): pointGroupArray, returns signature image as an array of point groups
• off(): void, unbinds all event handlers
• on(): void, rebinds all event handlers
• getCanvas(): canvas, returns the underlying canvas ref. Allows you to modify the canvas however you want or call methods such as toDataURL()
• getTrimmedCanvas(): canvas, creates a copy of the canvas and returns a trimmed version of it, with all whitespace removed.
• getSignaturePad(): SignaturePad, returns the underlying SignaturePad reference.

The API methods are mostly just wrappers around signature_pad's API. on() and off() will, in addition, bind/unbind the window resize event handler. getCanvas(), getTrimmedCanvas(), and getSignaturePad() are new.

Example

You can interact with the example in a few different ways:

1. Run npm start and navigate to http://localhost:1234/.
   Hosted locally via the example/ directory

2. View the live demo here.
   Hosted via the gh-pages branch, a standalone version of the code in example/

3. Play with the CodeSandbox here.
   Hosted via the codesandbox-example branch, a slightly modified version of the above.