# PostHog Browser JS Library

[![npm package](https://img.shields.io/npm/v/posthog-js?style=flat-square)](https://www.npmjs.com/package/posthog-js)
[![MIT License](https://img.shields.io/badge/License-MIT-red.svg?style=flat-square)](https://opensource.org/licenses/MIT)

For information on using this library in your app, [see PostHog Docs](https://posthog.com/docs/libraries/js).  
This README is intended for developing the library itself.

## dependencies

we use pnpm.

it's best to install using `npm install -g pnpm@latest-8`
and then `pnpm` commands as usual

## 

## Testing

Unit tests: run `pnpm test`.
Cypress: run `pnpm start` to have a test server running and separately `pnpm cypress` to launch Cypress test engine.

### Running TestCafe E2E tests with BrowserStack

Testing on IE11 requires a bit more setup. TestCafe tests will use the
playground application to test the locally built array.full.js bundle. It will
also verify that the events emitted during the testing of playground are loaded
into the PostHog app. By default it uses https://us.i.posthog.com and the
project with ID 11213. See the testcafe tests to see how to override these if
needed. For PostHog internal users ask @benjackwhite or @hazzadous to invite you
to the Project. You'll need to set `POSTHOG_API_KEY` to your personal API key, and
`POSTHOG_PROJECT_KEY` to the key for the project you are using.

You'll also need to sign up to [BrowserStack](https://www.browserstack.com/).
Note that if you are using CodeSpaces, these variables will already be available
in your shell env variables.

After all this, you'll be able to run through the below steps:

1. Optional: rebuild array.js on changes: `nodemon -w src/ --exec bash -c "pnpm build-rollup"`.
1. Export browserstack credentials: `export BROWSERSTACK_USERNAME=xxx BROWSERSTACK_ACCESS_KEY=xxx`.
1. Run tests: `npx testcafe "browserstack:ie" testcafe/e2e.spec.js`.

### Running local create react app example

You can use the create react app setup in `playground/nextjs` to test posthog-js as an npm module in a Nextjs application.

1. Run `posthog` locally on port 8000 (`DEBUG=1 TEST=1 ./bin/start`).
1. Run `python manage.py setup_dev --no-data` on posthog repo, which sets up a demo account.
1. Copy Project API key found in `http://localhost:8000/project/settings` and save it for the last step.
1. Run `cd playground/nextjs`.
1. Run `pnpm i` to install dependencies.
1. Run `pnpm run build-posthog-js` to build `posthog-js` locally.
1. Run `NEXT_PUBLIC_POSTHOG_KEY='<your-local-api-key>' NEXT_PUBLIC_POSTHOG_HOST='http://localhost:8000' pnpm dev` to start the application.

### Tiers of testing

1. Unit tests - this verifies the behavior of the library in bite-sized chunks. Keep this coverage close to 100%, test corner cases and internal behavior here
2. Cypress tests - integrates with a real chrome browser and is capable of testing timing, browser requests, etc. Useful for testing high-level library behavior, ordering and verifying requests. We shouldn't aim for 100% coverage here as it's impossible to test all possible combinations.
3. TestCafe E2E tests - integrates with a real posthog instance sends data to it. Hardest to write and maintain - keep these very high level

## Developing together with another project

Install pnpm to link a local version of `posthog-js` in another JS project: `npm install -g pnpm`

### Run this to link the local version

We have 2 options for linking this project to your local version: via [pnpm link](https://docs.npmjs.com/cli/v8/commands/npm-link) or via [local paths](https://docs.npmjs.com/cli/v9/configuring-npm/package-json#local-paths)

#### local paths (preferred)

- from whichever repo needs to require `posthog-js`, go to the `package.json` of that file, and replace the `posthog-js` dependency version number with `file:<relative_or_absolute_path_to_local_module>`
- e.g. from the `package.json` within `posthog`, replace `"posthog-js": "1.131.4"` with `"posthog-js": "file:../posthog-js"`
- run `pnpm install` from the root of the project in which you just created a local path

Then, once this link has been created, any time you need to make a change to `posthog-js`, you can run `pnpm build` from the `posthog-js` root and the changes will appear in the other repo.  

#### `pnpm link`

- In the `posthog-js` directory: `pnpm link --global`
- (for `posthog` this means: `pnpm link --global posthog-js && pnpm i && pnpm copy-scripts`)
- You can then remove the link by, e.g., running `pnpm link --global posthog-js` from within `posthog`

## Releasing a new version

Just put a `bump patch/minor/major` label on your PR! Once the PR is merged, a new version with the appropriate version bump will be released, and the dependency will be updated in [posthog/PostHog](https://github.com/posthog/PostHog) – automatically.
  
If you forget to add the label, don't try to update the version locally as you won't be able to push that commit to the main branch. Instead, just make a new PR.

### Prereleases

To release an alpha or beta version, you'll need to use the CLI locally:

#### CLI

Only one person is set as a collaborator on NPM, so they're the only person that can manually publish alphas

1. Make sure you're a collaborator on `posthog-js` in npm ([check here](https://www.npmjs.com/package/posthog-js)).
2. Make sure you're logged into the npm CLI (`npm login`).
3. Check out your work-in-progress branch (do not release an alpha/beta from `main`).
4. Run the following commands, using the same bump level (major/minor/patch) as your PR:

    ```bash
    npm version [premajor | preminor | prepatch] --preid=beta
    npm publish --tag beta
    git push --tags
    ```

5. Enjoy the new prerelease version. You can now use it locally, in a dummy app, or in the [main repo](https://github.com/posthog/PostHog).

#### Automagically

Use the "release alpha" label on your PR to have an alpha version published automatically. This automation currently doesn't check whether an alpha exists for the version it will try to publish. If you need to publish two alphas from one PR you'll need to fix that

Remember that these versions are public and folk might use them, so make sure they're not _too_ alpha 🙈
