ConstraintJS

ConstraintJS keeps values up to date automatically. A constraint is a value that can be computed from other constraints; when one of those changes, everything that depends on it updates. On top of that, ConstraintJS provides DOM bindings, finite-state machines, and a Handlebars-style template language whose output stays in sync with your data.

import cjs from "constraintjs";

const width = cjs(10);
const height = cjs(20);
const area = width.mul(height); // or: cjs(() => width.get() * height.get())

area.get(); // 200
width.set(15);
area.get(); // 300

// Keep the DOM in sync
cjs.bindText(document.getElementById("area"), "Area: ", area);

// ...or use a template
const box = cjs.createTemplate("<div>{{width}} × {{height}} = {{area}}</div>", { width, height, area });
document.body.append(box);
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For documentation and the full API, visit the ConstraintJS website and its API reference.

Installation

npm install constraintjs
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import cjs from "constraintjs"; // ES modules
const cjs = require("constraintjs"); // CommonJS
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Or load it with a <script> tag, which defines a global cjs:

<script src="https://cdn.jsdelivr.net/npm/constraintjs/dist/constraintjs.global.min.js"></script>
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ConstraintJS includes TypeScript types. Types can be imported by name (import cjs, { type Constraint } from "constraintjs") or used as cjs.Constraint<T>.

Development

You'll need Node.js 22.18 or later.

npm install
npm test            # run the tests (Vitest, in jsdom)
npm run build       # build dist/ (ES module, CommonJS, and <script> bundles, with types)
npm run check       # type-check, lint, check formatting, and test
npm run docs        # generate API documentation in docs/
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The source is in src/ (TypeScript) and the tests are in test/. npm run test:watch re-runs the tests as you edit, and npm run coverage reports test coverage.

The website is the gh-pages branch. To update it for a release, check that branch out somewhere and run npm run pages -- <path to the checkout>, which adds the new <script> bundles and API reference to it.

See CHANGELOG.md for what's changed.

License

MIT