Chai Assertion Library

Chai is a BDD / TDD assertion library for Node.js and the browser that can be delightfully paired with any JavaScript testing framework.

Download Chai

For Node

The chai package is available on npm.

npm install chai --save-dev

View Node Guide

For Browser

The chai.js script is available for download or a hotlink.

Download chai.js

View Browser Guide

Getting Started

Learn how to install and use Chai through a series of guided walkthroughs.

Getting Started Guide

API Documentation

Explore the BDD & TDD language specifications for all available assertions.

API Documentation

Plugin Directory

Extend Chai with additional assertions and vendor integration.

Plugin Directory

Interfaces

Chai has several interfaces that allow the developer to choose the most comfortable. The chain-capable BDD styles provide an expressive language & readable style, while the TDD assert style provides a more classical feel.

Should 

import "chai/register-should.js";

foo.should.be.a("string");
foo.should.equal("bar");
foo.should.have.lengthOf(3);
tea.should.have.property("flavors").with.lengthOf(3);

Visit Should Guide →

Expect 

import { expect } from "chai";

expect(foo).to.be.a("string");
expect(foo).to.equal("bar");
expect(foo).to.have.lengthOf(3);
expect(tea).to.have.property("flavors").with.lengthOf(3);

Visit Expect Guide →

Assert 

import { assert } from "chai";

assert.typeOf(foo, "string");
assert.equal(foo, "bar");
assert.lengthOf(foo, 3);
assert.property(tea, "flavors");
assert.lengthOf(tea.flavors, 3);

Visit Assert Guide →

Plugins

Plugins extend Chai's assertions to new contexts such as vendor integration & object construction. Developers can build their own plugins to share with the community or use the plugin pattern to DRY up existing tests.

Create expressive integration tests with Chai and selenium-webdriver.

import sw from "selenium-webdriver";
import { expect, use } from "chai";
import chaiWebdriver from "chai-webdriver";

const driver = new sw.Builder()
  .withCapabilities(sw.Capabilities.chrome())
  .build();

// And then...
use(chaiWebdriver(driver));

driver.get("http://chaijs.com/");
expect("nav h1").dom.to.contain.text("Chai");
expect("#node .button").dom.to.have.style("float", "left");

Learn More & Install →

Custom Plugins

Browse our growing directory of custom plugins & vendor integrations to find the best tool for your needs.

Browse Plugins →

Develop Plugins

Chai has an extensive utility belt for plugin developers. Learn how to build your plugins & share.

Plugin Guide →

Powered by Open Source

Chai is hosted on GitHub. Have a suggestion or found a bug? Fork this project to help make Chai even better. Even this documentation site is open source and available for contribution.

Fork Chai on GitHub →

Join our Community

We have an active GitHub Discussions forum where you can ask questions, discuss improvements, and contribute to Chai.

Visit GitHub Discussions →