JavaScript Signature Pad

@lemonadejs/signature · ✓ 23 contract checks · framework-agnostic · zero dependencies

<Signature /> — canvas signature pad, ported from the v5 plugin

Full behavioral parity with v5: pointer drawing (mouse + touch), the v5 value format (a flat list of [x, y] points with ‘1’ separators between strokes), line thickness, instructions text, disabled, and the full replay algorithm (commit): clear + redraw the whole value as one path — including the v5 quirk where a click stroke becomes a round dot.

v5 → v6 mapping: value (two-way) → bind; value (initial) stays value; line/width/height/instructions/disabled unchanged; onchange/onload unchanged (onchange now receives the value, not the instance); getValue/setValue/getImage move to the api surface (props.ref), plus clear() = setValue([]). New: color (v5 hardcoded #000), name (renders a hidden input so the pad participates in forms — v5 only patched .val() onto the canvas), and clearlabel (renders a real, keyboard-operable clear <button> — WCAG 2.1.1: clearing must not require a pointer).

Accessibility: drawing is a path-of-movement input (WCAG 2.1.1 essential-exception territory) — the canvas is exposed as role=“img” (“Signature pad”) and the host application should offer keyboard users an alternative (e.g. a typed signature) alongside the pad.

jsdom has no canvas: a null 2d context downgrades the pad to a no-op.

Example

live

LemonadeJS

import { html } from 'lemonadejs';
import Signature from '@lemonadejs/signature';

const App = (props, { state }) => {
    const strokes = state([]);
    const image = state('');
    let pad;

    return html`<div>
        <${Signature} bind="${strokes}" width="400" height="160" color="#1d4ed8"
            instructions="Sign here to accept the delivery" ref="${(api) => (pad = api)}" />
        <p>
            <button onclick="${() => { pad.clear(); image.value = ''; }}">Clear</button>
            <button onclick="${() => (image.value = pad.getImage())}">Export PNG</button>
            ${() => (strokes.value.length ? ' Signature captured (' + strokes.value.length + ' points)' : ' Waiting for a signature')}
        </p>
        ${() => (image.value ? html`<img src="${image.value}" alt="Signature" style="border:1px solid #ddd" />` : '')}
    </div>`;
};

Installation

npm install @lemonadejs/signature

import Signature from '@lemonadejs/signature';
import '@lemonadejs/signature/style.css';

Three deployment forms, one component:

html`<${Signature} />`                       // by value (no registration)
setComponents({ Signature });               // then <Signature /> by name anywhere
createWebComponent(Signature);              // <lm-signature> in plain HTML/any framework

Props

Every declared prop arrives as a live state — pass a value for a snapshot or a state for a two-way live wire. Attribute strings are coerced to the declared type.

Events

All event names are lowercase (the platform convention — LJS-305 warns otherwise).

• onchange — fires on stroke end, setValue and clear
• onload — fires once the canvas is ready (v5)

API

import { ref } from 'lemonadejs';
const signature = ref();
html`<${Signature} ref="${signature}" />`;
// signature.current.getValue(...)  ·  signature.current.setValue(...)  ·  signature.current.getImage(...)  ·  signature.current.clear(...)

• getValue()
• setValue()
• getImage()
• clear()

Styling

All classes follow the lm-signature-* convention; visual variants are data-* attributes on the root. Override freely — there is no styling engine to fight.

Contract

The machine-readable schema ships with the package:

import contract from '@lemonadejs/signature/contract.json';

verify.json carries the conformance proof produced by verify(Signature).

Looking for the v5 plugin? See the archived v5 documentation.