Checkly lets you use JavaScript / TypeScript in your Browser and Multistep checks, and in API check setup & teardown scripts. Checks are able to use NPM packages that are defined in our runtimes, as well as import local JavaScript and TypeScript files.

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NPM packages

Not all NPM packages from NPM are available inside the context of a Check.
The JavaScript code for checks executes in a runtime environment managed by Checkly. Runtime versions can be selected by setting a runtimeId. This can be configured at the check and group level using constructs, and a default value for the project can be set in the project configuration file. A runtime contains among others:
  • Nodejs v22+
  • @playwright/test 1.51.1
  • axios 0.28.0
  • lodash 4.17.21
  • moment 2.30.1
…and a range of other popular NPM package to help you write and assert checks.

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Local Dependencies

Your checks are also able to import other JavaScript and TypeScript files as dependencies. This is useful for defining helper functions to be reused across multiple checks. The Checkly CLI will automatically detect these dependencies and make sure that they’re bundled as part of the check. No additional configuration is needed. Here is a Browser Check example of how this works in practice. The directory tree looks like the following: 
__checks__
├── login.check.ts
├── login.spec.ts
└── login-helper.ts
login-helper.ts defines a function gitHubLogin that can be used by multiple Browser Checks.
login-helper.ts
export async function gitHubLogin (page, username, password) {
  await page.goto('https://github.com/login')
  await page.getByLabel('Username or email address').type(username)
  await page.getByLabel('Password').type(password)
  await page.getByRole('button', { name: 'Sign in' })
}
In login.spec.ts we define the actual Playwright test. This file can import the gitHubLogin function from login-helper.ts. It also reads the username and password from remote environment variables.
login.spec.ts
// @ts-ignore
import { test } from '@playwright/test'
import { gitHubLogin } from './login-helper'

test('Github login', async ({ page }) => {
  await gitHubLogin(page, process.env.GITHUB_USER, process.env.GITHUB_PWD)

  // your normal check code
  await page.click('.header-search-input')
})
login.check.ts initializes a new BrowserCheck construct. Note that it’s only necessary to configure the main Playwright file login.spec.ts. The login-helper.ts dependency is automatically detected by the CLI.
login.check.ts
import { BrowserCheck } from 'checkly/constructs'

new BrowserCheck('login-check', {
  name: 'Login Check',
    code: { entrypoint: './login.spec.ts' }
  })
})
After running npx checkly deploy, you can see in the Web UI that the helper file login-helper.ts was also uploaded for this Check. login check with helper file in dependencies The maximum total size of a Checkly project when deploying or running a test session, including local dependencies, is 40 MB.

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Why can’t I import any NPM package or other 3rd party dependencies?

Please see this paragraph in our runtime docs.