Javascript SDK

This is the official documentation for the Amplitude Analytics JavaScript SDK.

Install

Install the Amplitude Analytics JavaScript SDK in your project.

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      "setDeviceId",
      "enableTracking",
      "setGlobalUserProperties",
      "identify",
      "clearUserProperties",
      "setGroup",
      "logRevenueV2",
      "regenerateDeviceId",
      "groupIdentify",
      "onInit",
      "onNewSessionStart",
      "logEventWithTimestamp",
      "logEventWithGroups",
      "setSessionId",
      "resetSessionId",
      "getDeviceId",
      "getUserId",
      "setMinTimeBetweenSessionsMillis",
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  amplitude.getInstance().init(AMPLITUDE_API_KEY);
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After you've installed the SDK, import amplitude into your project.

import amplitude from "amplitude-js";

// initialize the client
var instance1 = amplitude.getInstance().init(AMPLITUDE_API_KEY);

// send an event
const event = "œButton Clicked";
amplitude.getInstance().logEvent(event);

Core functions

The following functions make up the core of the Amplitude Analytics JavaScript SDK.

Initialize

Before you can instrument, you must initialize the SDK using the API key for your Amplitude project.

Initialization creates a default instance, but you can create more instances using getInstance with a string name.

var instance1 = amplitude.getInstance().init("AMPLITUDE_API_KEY"); // initializes default instance of Amplitude client
var instance2 = amplitude
  .getInstance("instance-name")
  .init("AMPLITUDE_API_KEY"); // initializes named instance of Amplitude client

Initialization with options

Pass custom options in the init method. Refer to the list of options on GitHub.

var options = {};
var instance = amplitude
  .getInstance("instance")
  .init(AMPLITUDE_API_KEY, null, options); // initializes with the given options

Configuration

Configure batching behavior

To support high-performance environments, the SDK sends events in batches. The SDK queues every event that the logEvent method logs in memory. The SDK flushes events in batches in the background. You can customize batch behavior with eventUploadThreshold and eventUploadPeriodMillis. By default, the serverUrl is https://api.amplitude.com. This SDK doesn't support batch mode, the batch API endpoint.

amplitude.getInstance().init(apiKey, null, {
  // Events queued in memory will flush when number of events exceed upload threshold
  // Default value is 30
  eventUploadThreshold: 50,
  // Events queue will flush every certain milliseconds based on setting
  // Default value is 30000 milliseconds
  eventUploadPeriodMillis: 100000,
});

EU data residency

Starting with version 8.9.0, you can configure the server zone to send data to Amplitude's EU server after initializing the client.

The server zone configuration also supports dynamic configuration.

For earlier versions, configure the apiEndpoint property after initializing the client.

Version 8.9.0 and higherEarlier versions

// No need to call setServerUrl for sending data to Amplitude's EU servers
amplitude.getInstance().init(euApiKey, null, {
  serverZone: "EU",
  serverZoneBasedApi: true,
});

amplitude.getInstance().init(euApiKey, null, {
  apiEndpoint: "https://api.eu.amplitude.com",
});

Set userID

Set userID when initializing the client, or after initialization with the setUserId method.

var userId = "12345";
amplitude.getInstance().init(AMPLITUDE_API_KEY, userId); // initializes client with the given userId

Send events

Basic events

Events represent user interactions with your app. For example, "Button Clicked" might be an action you want to track.

const event = "Button Clicked";
amplitude.getInstance().logEvent(event);

Event properties

Events can have properties that give context about the event. For example, "œhover time" is a relevant property for the "Button Clicked" event.

var event = "Button Clicked";
var eventProperties = {
  "hover time": "100ms",
};
amplitude.getInstance().logEvent(event, eventProperties);

Arrays in event properties

Event property values can be arrays. You can query array event properties by any subset of the individual properties in the array.

var event = "Button Clicked";
var eventProperties1 = {
  selectedColors: ["red", "blue"],
};
amplitude.getInstance().logEvent(event, eventProperties1);

var eventProperties2 = {
  selectedColors: ["red", "green"],
};
amplitude.getInstance().logEvent(event, eventProperties2);

User properties

User properties help you understand your users at the time they performed some action within your app. For example, you can learn about their device details, their preferences, or language.

Set a user property

The Amplitude Identify object controls how you set user properties. First, create an Identify object instance, then call Identify methods on the instance, and then the client makes a call with the Identify object.

new amplitude.Identify(); // does nothing, must call one of the following methods and pass to client

var identify = new amplitude.Identify();
amplitude.getInstance().identify(identify); // makes identify call to amplitude with the properties of the identify object

set

Set the value of a user property. You can also chain together several set calls.

var identify1 = new amplitude.Identify().set("key1", "value1");
var identify2 = new amplitude.Identify()
  .set("key2", "value2")
  .set("key3", "value3");
amplitude.getInstance().identify(identify1);
amplitude.getInstance().identify(identify2);

setOnce

setOnce sets the value of a user property one time. Amplitude ignores subsequent calls using setOnce.

var identify = new amplitude.Identify().setOnce("key1", "value1");
amplitude.getInstance().identify(identify);

add

Increment a user property by a number with add. If the user property doesn't have a value set yet, it's initialized to 0.

var identify = new amplitude.Identify().add("value1", 10);
amplitude.getInstance().identify(identify);

Set multiple user properties

You can use setUserProperties as a shorthand to set multiple user properties at one time. For example, set a user's city with this code:

var userProperties = {
  city: "San Francisco",
};
amplitude.getInstance().setUserProperties(userProperties);

Arrays in user properties

User properties can be arrays. Directly set arrays or use append to generate an array.

var values = ["value1", "value2"];
var identify = new amplitude.Identify().set("key1", values);
amplitude.getInstance().identify(identify);

prepend and append

• append appends a value or values to a user property array.
• prepend prepends a value or values to a user property array.

If the user property doesn't have a value set yet, the SDK initializes it to an empty list before adding the new values. If the user property has an existing value and the value isn't a list, the SDK converts the value into a list and adds the new value.

User groups

Amplitude supports assigning users to groups and performing queries, such as Count by Distinct, on those groups. If at least one member of the group has performed the specific event, then the count includes the group.

For example, you want to group your users based on what organization they're in by using an 'orgId'. Joe is in 'orgId' '10', and Sue is in 'orgId' '15'. Sue and Joe both perform a certain event. You can query their organizations in the Event Segmentation Chart.

When setting groups, define a groupType and groupName. In the previous example, 'orgId' is the groupType and '10' and '15' are the values for groupName. Another example of a groupType could be 'sport' with groupName values like 'tennis' and 'baseball'.

Setting a group also sets the groupType:groupName as a user property, and overwrites any existing groupName value set for that user's groupType, and the corresponding user property value. groupType is a string, and groupName can be a string or an array of strings to indicate that a user belongs to multiple groups.

amplitude.getInstance().setGroup("orgId", ["10", "16"]);

You can also use logEventWithGroups to set event-level groups. With event-level groups, the group designation applies only to the specific event the SDK logs, and doesn't persist on the user unless you explicitly set it with setGroup.

var eventProperties = {
  key: "value",
};

amplitude
  .getInstance()
  .logEventWithGroups("initialize_game", eventProperties, { sport: "soccer" });

Group identify

Use the Group Identify API to set or update the properties of particular groups. Keep these considerations in mind:

• Updates affect only future events, and don't update historical events.
• You can track up to 5 unique group types and 10 total groups.

The groupIdentify method accepts a group type string parameter and group name object parameter, and an Identify object that the SDK applies to the group.

var groupType = "plan";
var groupName = "enterprise";
var identify = new amplitude.Identify().set("key1", "value1");

amplitude.getInstance().groupIdentify(groupType, groupName, identify);

You can supply an optional callback function as a fourth argument to groupIdentify.

Track revenue

The best method of tracking revenue for a user is to use logRevenueV2() with the provided Revenue interface. Revenue instances store each revenue transaction and let you define several special revenue properties that Amplitude's Event Segmentation and Revenue LTV charts use, such as revenueType and productIdentifier. You can also add event properties to revenue events through the eventProperties field. Pass these Revenue instance objects into logRevenueV2 to send them as revenue events to Amplitude. Amplitude then automatically displays data relevant to revenue in the platform. You can track both in-app and non-in-app purchases this way.

To track revenue from a user, call logRevenueV2() each time a user generates revenue. Here is an example:

var revenue = new amplitude.Revenue()
  .setProductId("com.company.productId")
  .setPrice(3.99)
  .setQuantity(3);
amplitude.getInstance().logRevenueV2(revenue);

Calling logRevenueV2 generates a revenue event type:

• [Amplitude] Revenue: The SDK logs this event for all revenue events, regardless of whether you enable verification.

You can't change the default names given to these client-side revenue events in the raw data, but you can change the display name. To learn more about tracking revenue, refer to Track revenue.

Opt users out of tracking

Call setOptOut to turn off logging for a given user:

amplitude.getInstance().setOptOut(true);

While setOptOut is enabled, the SDK doesn't save or send events to the server. The opt out setting persists across page loads. To re-enable logging, call:

amplitude.getInstance().setOptOut(false);

Disable tracking specific fields

By default, the JavaScript SDK tracks some properties automatically. You can override this behavior by passing an object called trackingOptions when initializing the SDK, setting the appropriate options to false.

Set custom user ID

If your app has its login system that you want to track users with, you can call setUserId at any time:

amplitude.getInstance().setUserId("USER_ID");

You can also add the User ID as an argument to the init call.

amplitude.getInstance().init(AMPLITUDE_API_KEY, "USER_ID");

Don't assign users a user ID that could change, because each unique user ID represents a unique user in Amplitude. For more information, refer to Track unique users in Amplitude in the Help Center.

Logged out and anonymous users

Amplitude merges user data, so Amplitude links any events associated with a known userId or deviceId to the existing user. If a user logs out, Amplitude can merge that user's logged-out events to the user's record. You can change this behavior and log those events to an anonymous user instead.

To log events to an anonymous user:

1. Set the userId to null.
2. Generate a new deviceId.

Events coming from the current user or device appear as a new user in Amplitude. Note: If you do this, you can't see that the two users used the same device.

amplitude.getInstance().setUserId(null); // not string 'null'
amplitude.getInstance().regenerateDeviceId();

Session tracking

Events triggered within 30 minutes of each other count toward the current session. The time of the first event marks the start time of a session, and the last triggered event marks the end time of a session. You can change the session timeout window through the SDK configuration option field sessionTimeout.

Get the session ID

In the JavaScript SDK, you can use the helper method getSessionId to get the value of the current sessionId:

const sessionId = amplitude.getInstance().getSessionId();

Configure HTTP headers

If you use a domain proxy that requires custom HTTP request headers, configure them with options.headers during initialization.

amplitude.getInstance().init(AMPLITUDE_API_KEY, null, {
  headers: {
    "x-session-id": appToken,
    "Content-Type": "application/json;charset=utf-8",
  },
});

Log events to multiple projects

If you want to log events to multiple Amplitude projects, you must have separate instances for each Amplitude project. Each instance allows for independent apiKeys, userIds, deviceIds, and settings.

You must assign a name to each Amplitude project and instance and use that name consistently when fetching that instance to call functions.

Instance names must be non-null and non-empty strings. Names are case insensitive, and you can fetch each instance by calling its name.

Each new instance has its own apiKey, userId, deviceId, and settings.

The following is an example of how to set up and log events to two separate projects:

// existing project, existing settings, and existing API key
amplitude.getInstance().init("12345", null, { batchEvents: true });
// new project, new API key
amplitude
  .getInstance("new_project")
  .init("67890", null, { includeReferrer: true });

// need to reconfigure new project
amplitude.getInstance("new_project").setUserId("joe@gmail.com");
amplitude.getInstance("new_project").setUserProperties({ gender: "male" });
amplitude.getInstance("new_project").logEvent("Clicked");

var identify = new amplitude.Identify().add("karma", 1);
amplitude.getInstance().identify(identify);
amplitude.getInstance().logEvent("Viewed Home Page");

Web attribution

Amplitude's JavaScript SDK doesn't ingest web attribution data by default, but setup is quick. The SDK can automatically ingest this information if you enable attribution configuration options.

Amplitude supports automatically tracking the following through the SDK configuration options:

• The 5 standard UTM parameters from the user's browser cookie or URL parameters by using includeUtm.
• The referring URL and domain from includeReferrer.
• Google Click Identifier from URL parameters through includeGclid.
• Facebook Click Identifier from URL parameters through includeFbclid.

Track UTM parameters

UTM parameters stand for Urchin Traffic Monitor parameters and help you analyze the effectiveness of different ad campaigns and referring sites. UTM parameters are case sensitive, so Amplitude treats them as different values if the capitalization varies.

There are five different standard UTM parameters:

• utm_source: This identifies which website sent the traffic (for example: Google, Facebook).
• utm_medium: This identifies the link type that was used (for example: banner, button, email).
• utm_campaign: This identifies a specific campaign used (for example: "summer_sale").
• utm_term: This identifies paid search terms used (for example: product+analytics).
• utm_content: This identifies what brought the user to the site and is commonly used for A/B testing (for example: "banner-link", "text-link").

Here is an example URL:

https://www.amplitude.com/?utm_source=newsletter&utm_campaign=product_analytics_playbook&utm_medium=email&utm_term=product%20analytics&utm_content=banner-link

Enable through the SDK

In Amplitude, after you set the includeUtm option to true, the JavaScript SDK automatically pulls UTM parameters from the referring URL and includes them as user properties on all relevant events:

• includeGclid: Gclid (Google Click Identifier) is a globally unique tracking parameter that Google uses. When in use, Google appends a unique parameter (for example: "?gclid=734fsdf3") to URLs at runtime. When you set this to true, the SDK captures initial_gclid and gclid as user properties.
• includeFbclid: Fbclid (Facebook Click Identifier) is a globally unique tracking parameter that Facebook uses. When in use, Facebook appends a unique parameter (for example: "?fbclid=392foih3") to URLs at runtime. When you set this to true, the SDK captures initial_fblid and fbclid as user properties.
• includeUtm: If true, finds the standard UTM parameters from either the URL or the browser cookie and sets them as user properties. This option sets utm_source, utm_medium, utm_campaign, utm_term, and utm_content, and initial_utm_source, initial_utm_medium, initial_utm_campaign, initial_utm_term, and initial_utm_content as user properties for the user. By default, the SDK captures UTM parameters once per session, and capture occurs when the user loads your site and the Amplitude SDK for the first time. You can disable the once per session restriction through the saveParamsReferrerOncePerSession configuration option. When the SDK detects that it should start a new session, the SDK pulls the UTM parameters that are available at the time. The SDK sets those UTM parameters as user properties, which persist for all the user's events going forward. However, the SDK captures initial UTM parameters one time for each user through a setOnce operation.

Track referrers

If you want to track how users are getting to your website, then track the referrer (the referring site).

Amplitude supports tracking these fields automatically:

• referrer: The last page the user was on (for example, <https://amplitude.com/behavioral-analytics-platform?ref=nav>).
• referring_domain: The domain that the user was last on (for example, amplitude.com).

Enable through the SDK

After you set the includeReferrer option to true, Amplitude captures the referrer and referring_domain for each session and sets them as user properties on relevant events:

• includeReferrer: When true, captures the referrer and referring_domain for each session as user properties, and the initial_referrer and initial_referring_domain user properties one time for each user. The referrer is the entire URL, while the referring_domain is the domain name where the user came from.

Amplitude captures initial referring information one time for each user through a setOnce operation.

First-touch attribution

Amplitude can capture the initial UTM parameters and referrer information for each user. Amplitude sets the first-touch attribution values when it detects a user's non-null UTM parameters for the first time. Amplitude sets these user properties one time:

• initial_utm_source
• initial_utm_medium
• initial_utm_campaign
• initial_utm_term
• initial_utm_content
• initial_referrer
• initial_referring_domain
• initial_gclid
• initial_fbclid

Capture these parameters by setting the JavaScript SDK configuration options includeReferrer, includeUtm, includeFbclid, and includeGclid to true.

Last-touch attribution

Amplitude captures where a user came from for each of their sessions by setting these user properties:

• utm_source
• utm_medium
• utm_campaign
• utm_term
• utm_content
• referrer
• referring_domain
• gclid
• fbclid

To use this, set the JavaScript SDK configuration options includeReferrer, includeUtm, includeFbclid, and includeGclid to true. By default, the SDK saves values only at the start of the session, so if a user triggers some flow that causes them to land on the site again with a different set of UTM parameters within the same session, the SDK doesn't save the second set.

Multi-touch attribution

If you set saveParamsReferrerOncePerSession to false in your JavaScript SDK configuration, the SDK always captures new values from the user. This updates these user properties throughout a session if they change:

• utm_source
• utm_medium
• utm_campaign
• utm_term
• utm_content
• referrer
• referring_domain
• gclid
• fbclid

Some customers also instrument these user properties as arrays to track all the attribution parameters that the SDK detects within the same session for a single user.

Log captured attribution values through Amplitude

This is an advanced use case.

If you set logAttributionCapturedEvent to true in your JavaScript SDK configuration, the SDK logs an Amplitude event whenever it captures new attribution values from the user.

Event Name: [Amplitude] Attribution Captured

Event Properties:

• utm_source
• utm_medium
• utm_campaign
• utm_term
• utm_content
• referrer
• referring_domain
• gclid
• fbclid

Google Tag Manager

Amplitude's JavaScript SDK supports integration with Google Tag Manager. Refer to the demo app on GitHub for setup instructions.

Troubleshooting and debugging

How to debug

Debugging in a browser can help you identify problems related to your code's implementation, and potential issues within the SDKs you're using. Here's a basic guide on how to use the browser's built-in Developer Tools (DevTools) for debugging.

Console

You can find JavaScript errors under Inspect > Console, which might have the details about the line of code and file that caused the problem. The console also lets you execute JavaScript code in real time.

• Enable debug mode by following these instructions. With the default logger, the SDK outputs extra function context information to the developer console whenever you invoke any SDK public method, which can help with debugging.
• Amplitude supports SDK deferred initialization. The SDK dispatches events tracked before initialization after the initialization call. If you can't send events but can send the event successfully after entering amplitude.init(API_KEY, 'USER_ID') in the browser console, your amplitude.init call might not have triggered in your codebase, or you aren't using the correct amplitude instance during initialization. Check your implementation.

Instrumentation Explorer/Chrome Extension

The Amplitude Instrumentation Explorer is an extension available in the Google Chrome Web Store. The extension captures each Amplitude event you trigger and displays it in the extension popup. Confirm that the SDK sent the event successfully, and check the context in the event payload.

Common issues

The following are common issues specific to Browser SDK.

AD Blocker

Ad Blocker might lead to event dropping. The following errors indicate that Ad Blocker affects tracking. When you load through a script tag, an error might appear in the console/network tab while the SDK script loads. When you load with the npm package, errors might appear in the network tab when the SDK tries to send events to the server. The errors might vary depending on the browser.

• Chrome (Ubuntu, MacOS) Console: error net::ERR_BLOCKED_BY_CLIENT Network: status (blocked:other)
• Firefox (Ubuntu) Console: error text doesn"™t contain any blocking-specific info Network: Transferred column contains the name of plugin Blocked by uBlock Origin
• Safari (MacOS) Console: error contains text Content Blocker prevented frame ... from loading a resource from ... Network: it looks like blocked requests aren't listed. Not sure if it"™s possible to show them.

Amplitude recommends using a proxy server to avoid this situation.

Cookies related

Refer to the cookie management for the information the SDK stores in cookies. Client behavior, like disabling cookies or using a private browser/window/tab, affects the persistence of these saved values in the cookies. If these values aren't persistent or aren't increasing by one, that could be the reason.

CORS

Cross-Origin Resource Sharing (CORS) is a security measure that browsers use to restrict how a web page can request resources from a different domain. CORS might cause this issue if you used setServerURL.

Access to fetch at 'xxx' from origin 'xxx' has been blocked by CORS policy: Response to preflight request doesn't pass access control check: No 'Access-Control-Allow-Origin' header is present on the requested resource. If an opaque response serves your needs, set the request's mode to 'no-cors' to fetch the resource with CORS disabled.

Cross-origin resource sharing (CORS) prevents a malicious site from reading another site's data without permission. The error message indicates that the server you're trying to access doesn't allow your origin to access the requested resource. The cause is the missing Access-Control-Allow-Origin header in the server's response.

• If you have control over the server, you can update the server's CORS policy. Add the Access-Control-Allow-Origin header to the server's responses. This change allows your origin to make requests. The value of Access-Control-Allow-Origin can be * to allow all origins, or the specific URL of your web page.
• If you don't have control over the server, you can set up a proxy server that adds the necessary CORS headers. The web page makes requests to the proxy, which then makes requests to the actual server. The proxy adds the Access-Control-Allow-Origin header to the response before sending it back to the web page.

If you set up an API proxy and run into configuration issues related to that on a platform you"™ve selected, that"™s no longer an SDK issue but an integration issue between your application and the service provider.

Events fired but no network requests

If you set the logger to "Debug" level, and see track calls in the developer console, the SDK called the track() method. If you don't see the corresponding event in Amplitude, the Amplitude Instrumentation Explorer Chrome extension, or the network request tab of the browser, the SDK didn't send the event to Amplitude. The SDK fires events and places them in the SDK's internal queue after a successful track() call, but sometimes these queued events might not send successfully. This can happen when the browser cancels an in-progress HTTP request. For example, if you close the browser or leave the page.

There are two ways to address this issue:

1. If you use standard network requests, set the transport to beacon during initialization or set the transport to beacon upon page exit. sendBeacon doesn't work in this case because it sends events in the background, and doesn't return server responses like 4xx or 5xx. As a result, it doesn't retry on failure. sendBeacon sends only scheduled requests in the background. For more information, refer to the sendBeacon section.
2. To make track() synchronous, add the await keyword before the call.

Advanced topics

Dynamic configuration

Starting with version 8.9.0, you can configure your apps to use dynamic configuration. This feature finds the best server URL automatically based on app users' location.

To use, set useDynamicConfig to true.

• If you have your own proxy server and use the apiEndPoint API, leave dynamic configuration off.
• If you have users in China Mainland, Amplitude recommends using dynamic configuration.
• By default, this feature returns the server URL of Amplitude's US servers. If you need to send data to Amplitude's EU servers, use setServerZone to set it to EU zone.

amplitude.getInstance().init(euApiKey, null, {
  useDynamicConfig: true,
});

COPPA control

COPPA control in Amplitude's other SDKs disables tracking for IDFA, IDFV, city, location data (location_lat and location_lng), and IP address. The JavaScript SDK has no interface for COPPA control because the SDK doesn't track location_lat, location_lng, IDFA, or IDFV. Instead, you can disable tracking for city and ip_address with trackingOptions.

var trackingOptions = {
  city: false,
  ip_address: false,
};

Get the device ID

Get a user's current device ID with the following code:

var deviceId = amplitude.getInstance().getDeviceId(); // existing device ID

Set configuration options

Configure Amplitude by passing an object as the third argument to the init:

amplitude.getInstance().init(AMPLITUDE_API_KEY, null, {
  // optional configuration options
  saveEvents: true,
  includeUtm: true,
  includeReferrer: true,
});

Cookie management

Cookies created by the SDK

On initialization, the SDK creates a cookie that begins with the prefix amp_ and ends with the first six digits of your API key. For example, amplitude.getInstance().init("a2dbce0e18dfe5f8e74493843ff5c053") creates a cookie with the key amp_a2dbce.

The cookie tracks this metadata for the SDK:

• A randomly generated device ID
• The current session ID
• The current user ID if a user ID is set
• The last event time
• Sequence IDs to put events and identify operations in the correct order

Disable cookies

Disable cookies created by the SDK with the disableCookies option. When you disable cookies, the JavaScript SDK defaults to using localStorage to store its data. LocalStorage is a useful alternative, but can't track cookies across domains. Because the browser restricts access to localStorage by subdomain, you can't track anonymous users across subdomains of your product (for example: www.amplitude.com versus analytics.amplitude.com).

SameSite

The JavaScript SDK defaults to setting the SameSite option on its cookies to None. This can be overridden with the sameSiteCookie option. Amplitude recommends using Lax unless there are instances where you have third party sites that POST forms to your site.

HTTPOnly cookies

An HTTPOnly option isn't technologically possible for cookies that the SDK creates. The SDK sets the cookie on the client side and uses it as a client-side data store. An SDK cookie can't set the HTTPOnly flag.

Upgrade legacy cookies

Legacy cookies that the SDK created were larger than the newer, more compact cookies. For users that have older cookies, the SDK only removes old cookies and starts using the new cookie format if the cookieForceUpgrade option is set to true. If you use the SDK in multiple products, and track anonymous users across those products, you be sure to set this option on all those products.

RequireJS

If you use RequireJS to load your JavaScript files, you can use it to load the Amplitude JavaScript SDK script directly instead of using the loading snippet. If you take this approach, you lose one of the key advantages of the snippet, which lets your app start and use the Amplitude SDK without waiting for Amplitude to fully download.

<script src="scripts/require.js"></script>
<!-- loading RequireJS -->
<script>
  require([
    "https://cdn.amplitude.com/libs/amplitude-6.2.0-min.umd.gz.js",
  ], function (amplitude) {
    amplitude.getInstance().init(AMPLITUDE_API_KEY); // replace AMPLITUDE_API_KEY with your Amplitude API key.
    window.amplitude = amplitude; // You can bind the amplitude object to window if you want to use it directly.
    amplitude.getInstance().logEvent("Clicked Link A");
  });
</script>

You can also define the path in your RequireJS configuration like this:

<script src="scripts/require.js"></script>
<!-- loading RequireJS -->
<script>
  requirejs.config({
    paths: {
      amplitude: "https://cdn.amplitude.com/libs/amplitude-6.2.0-min.umd.gz.js",
    },
  });

  require(["amplitude"], function (amplitude) {
    amplitude.getInstance().init(AMPLITUDE_API_KEY); // replace AMPLITUDE_API_KEY with your Amplitude API key.
    window.amplitude = amplitude; // You can bind the amplitude object to window if you want to use it directly.
    amplitude.getInstance().logEvent("Clicked Link A");
  });
</script>
<script>
  require(["amplitude"], function (amplitude) {
    amplitude.getInstance().logEvent("Page loaded");
  });
</script>

Cross-domain tracking (JavaScript)

You can track anonymous behavior across two different domains. Amplitude identifies anonymous users by their device IDs, which you must pass between the domains. For example:

• Site 1: www.example.com
• Site 2: www.example.org

Users who start on Site 1 and then navigate to Site 2 must have the device ID generated from Site 1 passed as a parameter to Site 2. Site 2 then needs to initialize the SDK with the device ID. The SDK can parse the URL parameter automatically if deviceIdFromUrlParam is enabled.

1. From Site 1, grab the device ID from amplitude.getInstance().options.deviceId.
2. Pass the device ID to Site 2 through a URL parameter when the user navigates. (for example: www.example.com?amp_device_id=device_id_from_site_1)
3. Initialize the Amplitude SDK on Site 2 with amplitude.init(AMPLITUDE_API_KEY, null, {deviceIdFromUrlParam: true}).

Tracking UTM parameters, referrer, and gclid (JavaScript)

Amplitude supports automatically tracking:

• Standard UTM parameters from the user's cookie or URL parameters when the configuration option includeUtm is set to true during initialization.
• The referring URL when the configuration option includeReferrer is set to true during initialization.
• gclid (Google Click ID) from URL parameters when the configuration option includeGclid is set to true during initialization.

If you enable tracking, the SDK sets the values as user properties (for example, referrer or utm_source) one time per session. This is called last touch attribution. The SDK also saves the initial values like initial_referrer and initial_utm_source using a setOnce operation. After the SDK sets these values, they never change. This is called first touch attribution.

saveParamsReferrerOncePerSession

By default, the SDK saves the values only at the start of the session. For example, if a user lands on your site with an initial set of UTM parameters and triggers some flow that causes them to land on your site again with a different set of UTM parameters within the same Amplitude session, the SDK doesn't save the second set. You can set the configuration option saveParamsReferrerOncePerSession to false to remove that restriction so that the SDK always captures new values from the user.

unsetParamsReferrerOnNewSession

By default, the SDK carries over existing UTM Parameters and Referrer values at the start of a new session. For example, if a user's session expires, the SDK maps the user's Referrer and UTM Parameters to existing values. To reset those values to null when the SDK instantiates a new session, set unsetParamsReferrerOnNewSession to true.

Callbacks for logEvent, identify, and redirect

You can pass a callback function to logEvent and identify, which the SDK calls after receiving a response from the server. This is useful if timing might cause the SDK to miss capturing an event before the browser navigates away from a webpage. Putting the navigation in a callback to the logEvent method guarantees the SDK captures the event before navigation occurs. Here is a logEvent example:

amplitude.getInstance().logEvent("EVENT_TYPE", null, callback_function);

Here is an identify example:

var identify = new amplitude.Identify().set("key", "value");
amplitude.getInstance().identify(identify, callback_function);

The SDK passes the status and response body from the server to the callback function, which you might find useful. Here is an example of a callback function that redirects the browser to another site after a response:

var callback_function = function (status, response) {
  if (status === 200 && response === "success") {
    // do something here
  }
  window.location.replace("URL_OF_OTHER_SITE");
};

You can also use this to track outbound links to your website. For example, you would have a link like this:

<a href="javascript:trackClickLinkA();">Link A</a>

Then, define a function that runs when the user clicks the link like this:

var trackClickLinkA = function () {
  amplitude.getInstance().logEvent("Clicked Link A", null, function () {
    window.location = "LINK_A_URL";
  });
};

When optOut is true, the SDK doesn't log the event, but it still calls the callback. When batchEvents is true, if the batch requirements eventUploadThreshold and eventUploadPeriodMillis aren't met when you call logEvent, the SDK doesn't send a request, but it still calls the callback. In these cases, the SDK calls the callback with an input status of 0 and a response of 'No request sent'.

Error callbacks

You can pass a second callback to logEvent and identify that the SDK calls if the network request for the event fails. This is useful to detect if a user is using an ad blocker, or if there's an error from the Amplitude server because of an issue with the event format. You can use the error callback together with the success callback like this:

var successCallback = function () {
  console.log("the event was logged successfully");
};

var errorCallback = function () {
  console.log("there was an error logging the event");
};

amplitude.getInstance().logEvent("event", null, successCallback, errorCallback);

init callbacks

You can also pass a callback function to init, which the SDK calls after it finishes its asynchronous loading. The SDK passes the instance as an argument to the callback:

amplitude
  .getInstance()
  .init(AMPLITUDE_API_KEY, "USER_ID", null, function (instance) {
    console.log(instance.options.deviceId); // access Amplitude's deviceId after initialization
  });

Use sendBeacon

In SDK version 8.5.0 and higher, the SDK can send events using the browser's built-in navigator.sendBeacon API. Unlike standard network requests, sendBeacon sends events in the background, even when the user closes the browser or leaves the page.

To send an event using sendBeacon, set the transport SDK option to 'beacon' in one of two ways

// set transport to 'beacon' when initializing an event
amplitude
  .getInstance()
  .init(AMPLITUDE_API_KEY, "USER_ID", { transport: "beacon" });

// set transport to 'beacon' after initialization
amplitude.getInstance().setTransport("beacon");

// this event will be sent using navigator.sendBeacon
amplitude.getInstance().logEvent("send event with beacon");

// set transport back to the default 'http' value
amplitude.getInstance().setTransport("http");

// this event will be sent using the standard xhr mechanism
amplitude.getInstance().logEvent("send event with http");

Use sendBeacon only when exiting page

The JavaScript SDK provides a callback function that runs only when the user exits the page. It automatically switches the transport to 'beacon' for any logs sent in the callback. This callback is called onExitPage, and you pass it into the SDK on initialization, like so:

var exitCallback = function {
 amplitude.getInstance().logEvent('Logging a final event as user exits via sendBeacon');
};

amplitude.getInstance().init(AMPLITUDE_API_KEY, 'USER_ID', { onExitPage: exitCallback });

Device ID lifecycle

The SDK initializes the device ID in the following order, setting the device ID to the first valid value it encounters:

1. Device id in configuration on initialization.
2. "amp_device_id" value from URL param if configuration.deviceIdFromUrlParam is true. Refer to cross domain tracking for more details.
3. Device id in cookie storage. Refer to cookie management for more details.
4. A randomly generated 22-character base64 ID. This ID is more compact than a 36-character UUID, which has the same 128-bit range.

When does a device ID change

A device ID changes in many scenarios:

Amplitude Analytics SDKs share an identity store with Experiment SDKs.

setDeviceId also updates the identity store to propagate new user info to the experiment SDK and trigger a fetch if the device ID changes.

• You call setDeviceId() explicitly.
• By default the SDK stores device IDs in cookies, so a device ID changes if a user clears cookies, uses another device, or uses privacy mode.
• On initialization, the SDK takes a device ID from the URL param amp_device_id when deviceIdFromUrlParam is enabled.

Custom device ID

You can assign a new device ID using setDeviceId(). When setting a custom device ID, make sure the value is sufficiently unique. Amplitude recommends using a UUID.

By default, the device ID is a randomly generated base64 ID. You can define a custom device ID by setting it as a configuration option or by calling setDeviceId.

amplitude.getInstance().setDeviceId("DEVICE_ID");

Get device ID

You can retrieve the device ID that Amplitude uses with Amplitude.getInstance().getDeviceId() or Amplitude.getInstance('YOUR-INSTANCE-NAME').getDeviceId() if you defined a custom instance name. This method can return null if the SDK hasn't generated a deviceId yet.

const deviceId = amplitude.getInstance().getDeviceId();

Share current device ID to another instance

Sometimes you have more than one Amplitude JavaScript SDK instance set up and want to share the device ID across instances.

• Method1: Initialize the other instance with device ID in configuration

// Initialize an instance with default configuration
// Device Id of this instance is created by default
var instanceDev = amplitude.getInstance("amplitude-dev");
instanceDev.init("API-KEY-1");

// Initialize another instance with a different API key
// And pass the deviceId from the previous instance to the configuration
var instanceProd = amplitude.getInstance("amplitude-prod");
instanceProd.init("API-KEY-2", undefined, {
  deviceId: instanceDev.getDeviceId(),
});

• Method2: Set device ID after initialization whenever you need it to be the same

var instanceDev = amplitude.getInstance("amplitude-dev");
instanceDev.init("API-KEY-1");

var instanceProd = amplitude.getInstance("amplitude-prod");
instanceProd.init("API-KEY-2");

// Before the line blow, the device Ids of the two instances are different
instanceProd.setDeviceId(instanceDev.getDeviceId());

• Method3: Pass the device ID in URL param amp_device_id. Refer to cross domain tracking for more details.

Content Security Policy (CSP)

If your web app configures the strict Content Security Policy (CSP) for security concerns, adjust the policy to allow the Amplitude domains:

• When using "Snippet", add https://*.amplitude.com to script-src.
• Add https://*.amplitude.com to connect-src.