PostHog
PostHog Browser JS Library
For information on using this library in your app, see PostHog Docs.
This README is intended for developing the library itself.
Dependencies
we use pnpm.
it's best to install using npm install -g pnpm@latest-9
and then pnpm commands as usual
Optional Dependencies
This package has the following optional peer dependencies:
@rrweb/types(2.0.0-alpha.17): Only required if you're using Angular Compiler and need type definitions for the rrweb integration.rrweb-snapshot(2.0.0-alpha.17): Only required if you're using Angular Compiler and need type definitions for the rrweb integration.
These dependencies are marked as optional to reduce installation size for users who don't need these specific features.
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Testing
[!NOTE] Run
pnpm buildat least once before running tests.
- Unit tests: run
pnpm test. - Cypress: run
pnpm startto have a test server running and separatelypnpm cypressto launch Cypress test engine. - Playwright: run e.g.
pnpm exec playwright test --ui --project webkit --project firefoxto run with UI and in webkit and firefox
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. 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:
- Optional: rebuild array.js on changes:
nodemon -w src/ --exec bash -c "pnpm build-rollup". - Export browserstack credentials:
export BROWSERSTACK_USERNAME=xxx BROWSERSTACK_ACCESS_KEY=xxx. - 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.
- Run
posthoglocally on port 8000 (DEBUG=1 TEST=1 ./bin/start). - Run
python manage.py setup_dev --no-dataon posthog repo, which sets up a demo account. - Copy Project API key found in
http://localhost:8000/project/settingsand save it for the last step. - Run
cd playground/nextjs. - Run
pnpm ito install dependencies. - Run
pnpm run build-posthog-jsto buildposthog-jslocally. - Run
NEXT_PUBLIC_POSTHOG_KEY='<your-local-api-key>' NEXT_PUBLIC_POSTHOG_HOST='http://localhost:8000' pnpm devto start the application.
Tiers of testing
- 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
- Browser tests - run in real browsers and so 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.
- 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 or via local paths
local paths (preferred)
- from whichever repo needs to require
posthog-js, go to thepackage.jsonof that file, and replace theposthog-jsdependency version number withfile:<relative_or_absolute_path_to_local_module> - e.g. from the
package.jsonwithinposthog, replace"posthog-js": "1.131.4"with"posthog-js": "file:../posthog-js" - run
pnpm installfrom 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-jsdirectory:pnpm link --global - (for
posthogthis 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-jsfrom withinposthog
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 – 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
- Make sure you're a collaborator on
posthog-jsin npm (check here). - Make sure you're logged into the npm CLI (
npm login). - Check out your work-in-progress branch (do not release an alpha/beta from
main). Run the following commands, using the same bump level (major/minor/patch) as your PR:
npm version [premajor | preminor | prepatch] --preid=beta npm publish --tag beta git push --tagsEnjoy the new prerelease version. You can now use it locally, in a dummy app, or in the main repo.
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 🙈