Session replay installation

Session replay enables you to record users navigating through your website or mobile app and play back the individual sessions to watch how real users use your product.

Step one: Install our JavaScript web library

If you already have our JavaScript library or snippet installed, you can skip this step.

Option 1: Add the JavaScript snippet to your HTML Recommended

HTML
<script>
    !function(t,e){var o,n,p,r;e.__SV||(window.posthog=e,e._i=[],e.init=function(i,s,a){function g(t,e){var o=e.split(".");2==o.length&&(t=t[o[0]],e=o[1]),t[e]=function(){t.push([e].concat(Array.prototype.slice.call(arguments,0)))}}(p=t.createElement("script")).type="text/javascript",p.crossOrigin="anonymous",p.async=!0,p.src=s.api_host.replace(".i.posthog.com","-assets.i.posthog.com")+"/static/array.js",(r=t.getElementsByTagName("script")[0]).parentNode.insertBefore(p,r);var u=e;for(void 0!==a?u=e[a]=[]:a="posthog",u.people=u.people||[],u.toString=function(t){var e="posthog";return"posthog"!==a&&(e+="."+a),t||(e+=" (stub)"),e},u.people.toString=function(){return u.toString(1)+".people (stub)"},o="init capture register register_once register_for_session unregister unregister_for_session getFeatureFlag getFeatureFlagPayload isFeatureEnabled reloadFeatureFlags updateEarlyAccessFeatureEnrollment getEarlyAccessFeatures on onFeatureFlags onSessionId getSurveys getActiveMatchingSurveys renderSurvey canRenderSurvey getNextSurveyStep identify setPersonProperties group resetGroups setPersonPropertiesForFlags resetPersonPropertiesForFlags setGroupPropertiesForFlags resetGroupPropertiesForFlags reset get_distinct_id getGroups get_session_id get_session_replay_url alias set_config startSessionRecording stopSessionRecording sessionRecordingStarted captureException loadToolbar get_property getSessionProperty createPersonProfile opt_in_capturing opt_out_capturing has_opted_in_capturing has_opted_out_capturing clear_opt_in_out_capturing debug".split(" "),n=0;n<o.length;n++)g(u,o[n]);e._i.push([i,s,a])},e.__SV=1)}(document,window.posthog||[]);
    posthog.init('<ph_project_api_key>',{api_host:'https://us.i.posthog.com', defaults:'2025-05-24'})
</script>

Option 2: Install via package manager

npm install --save posthog-js

And then include it with your project API key and host (which you can find in your project settings):

Web
import posthog from 'posthog-js'


posthog.init('<ph_project_api_key>', {
  api_host: 'https://us.i.posthog.com',
  defaults: '2025-05-24'
})

See our framework specific docs for Next.js, React, Vue, Angular, Astro, Remix, and Svelte for more installation details.

Bundle all required extensions (advanced)

By default, the JavaScript Web library only loads the core functionality. It lazy-loads extensions such as surveys or the session replay 'recorder' when needed.

This can cause issues if:

  • You have a Content Security Policy (CSP) that blocks inline scripts.
  • You want to optimize your bundle at build time to ensure all dependencies are ready immediately.
  • Your app is running in environments like the Chrome Extension store or Electron that reject or block remote code loading.

To solve these issues, we have multiple import options available below.

Note: With any of the no-external options, the toolbar will be unavailable as this is only possible as a runtime dependency loaded directly from us.posthog.com.

Web
// No external code loading possible (this disables all extensions such as Replay, Surveys, Exceptions etc.)
import posthog from 'posthog-js/dist/module.no-external'


// No external code loading possible but all external dependencies pre-bundled
import posthog from 'posthog-js/dist/module.full.no-external'


// All external dependencies pre-bundled and with the ability to load external scripts (primarily useful is you use Site Apps)
import posthog from 'posthog-js/dist/module.full'


// Finally you can also import specific extra dependencies 
import "posthog-js/dist/recorder"
import "posthog-js/dist/surveys"
import "posthog-js/dist/exception-autocapture"
import "posthog-js/dist/tracing-headers"
import "posthog-js/dist/web-vitals"
import posthog from 'posthog-js/dist/module.no-external'


// All other posthog commands are the same as usual
posthog.init('<ph_project_api_key>', { api_host: 'https://us.i.posthog.com', defaults: '2025-05-24' })

Note: You should ensure if using this option that you always import posthog-js from the same module, otherwise multiple bundles could get included. At this time @posthog/react does not work with any module import other than the default.

Don't want to send test data while developing?

If you don't want to send test data while you're developing, you can do the following:

Web
if (!window.location.host.includes('127.0.0.1') && !window.location.host.includes('localhost')) {
    posthog.init('<ph_project_api_key>', { api_host: 'https://us.i.posthog.com', defaults: '2025-05-24' })
}
What is the `defaults` option?

The defaults is a date, such as 2025-05-24, for a configuration snapshot used as defaults to initialize PostHog. This default is overridden when you explicitly set a value for any of the options.

Step two: Enable session recordings in your project settings

Enable session recordings in your PostHog Project Settings.

Enable session recordings in your PostHog'

Once enabled, the library will start recording sessions by default.

They can be toggled off in the by setting the disable_session_recording: true flag in the config.

Users who opt out of event capturing will not have their sessions recorded.

Note on using Segment's SDK: Session Replay does not work if you send data using Segment's SDK as this data is not collected. If you use Segment, you may want to add the PostHog library as well – (make sure to only send regular event data from one source).

How to ignore sensitive elements

You may want to hide sensitive text or elements in your replays. See our privacy controls docs for how to do this.

How to record sessions across different domains

PostHog automatically captures sessions across subdomains (e.g. posthog.com and us.posthog.com), but recording sessions across different domains (e.g. posthog.com and hogflix.com) requires a bit more setup.

To do this, you need to pass the session_id from the first domain to the second domain (for example, as a URL parameter). You can get this value by calling posthog.get_session_id().

Below is an example of how this looks like in Next.js:

JavaScript
// first domain
'use client'
import { usePostHog } from '@posthog/react'


export default function FirstDomain() {
  const posthog = usePostHog()
  return (
    <div>
      <h1>Welcome to the first domain</h1>
      <button onClick={
        () => window.location.href = `https://seconddomain.com/?session_id=${posthog.get_session_id()}`
      }>
        Go to the second domain
      </button>
    </div>
  )
}

On the second domain, bootstrap the PostHog initialization using the session ID.

JavaScript
// second domain
'use client'
import posthog from 'posthog-js'
import { PostHogProvider } from '@posthog/react'
import { useSearchParams } from 'next/navigation'


export function PHProvider({ children }) {
  const searchParams = useSearchParams()
  const sessionID = searchParams.get('session_id')


  if (typeof window !== 'undefined') {
    posthog.init('<ph_project_api_key>', {
      api_host: 'https://us.i.posthog.com',
      defaults: '2025-05-24',
      bootstrap: { sessionID }
    })
  }


  return <PostHogProvider client={posthog}>{children}</PostHogProvider>
}

With this setup, PostHog tracks the user's session across domains and captures a single, combined replay.

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