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Node.js Server SDK for Statsig

Statsig server SDK for Node JS applications. This SDK is open source and hosted on github.

The Basics

Get started in a few quick steps.

  1. Create a free account on
  2. Install the SDK
  3. Initialize the SDK
  4. Fetch Feature Gates, Dynamic Configs, or Experiments
  5. Log a custom event

Step 1 - Create a free account on

You could skip this for now, but you will need an SDK Key and some Feature Gates or Dynamic Configs to use with the SDK in just a minute.

Step 2 - Install the SDK

The Node.js SDK is hosted here. You can install the SDK using NPM or Yarn:

npm install statsig-node

Step 3 - Initialize the SDK

After installation, you will need to initialize the SDK using a Server Secret Key from the statsig console.


Do NOT embed your Server Secret Key in client side applications, or expose it in any external facing documents. However, if you accidentally exposed it, you can create a new one in Statsig console.

There is also an optional parameter options that allows you to pass in a StatsigOptions to customize the SDK.

const statsig = require('statsig-node');

await statsig.initialize(
{ environment: { tier: 'staging' } }, // optional, pass options here if needed

initialize will perform a network request. After initialize completes, virtually all SDK operations will be synchronous1--the SDK will fetch updates from Statsig in the background, independently of your API calls.

Step 4 - Fetch Feature Gates, Dynamic Configs, or Experiments

Now that your SDK is initialized, let's fetch a Feature Gate. Feature Gates can be used to create logic branches in code that can be rolled out to different users from the Statsig Console. Gates are always CLOSED or OFF (think return false;) by default.

From this point on, all APIs will require you to specify the user (see Statsig user) associated with the request. For example, check a gate for a certain user like this:

const user = {
userID: '12345',
email: '',

const showNewDesign = await statsig.checkGate(user, 'new_homepage_design');
if (showNewDesign) {
// show new design here
} else {
// show old design here

Feature Gates can be very useful for simple on/off switches, with optional but advanced user targeting. However, if you want to be able send a different set of values (strings, numbers, and etc.) to your clients based on specific user attributes, e.g. country, Dynamic Configs can help you with that. The API is very similar to Feature Gates, but you get an entire json object you can configure on the server and you can fetch typed parameters from it. For example:

const config = await statsig.getConfig(user, "awesome_product_details");

// The 2nd parameter is the default value to be used in case the given parameter name does not exist on
// the Dynamic Config object. This can happen when there is a typo, or when the user is offline and the
// value has not been cached on the client.
const itemName = config.get("product_name", "Awesome Product v1");
const price = config.get("price", 10.0);
const shouldDiscount = config.get("discount", false);

Then we have Experiments, which you can use to run A/B/n experiments and use advanced features like layers (coming soon) to avoid collision and enable quicker iterations with parameter reuse.

const expConfig = await statsig.getExperiment(user, "new_user_promo");

const promoTitle = expConfig.get("title", "Welcome to Statsig! Use discount code WELCOME10OFF for 10% off your first purchase!");
const discount = expConfig.get("discount", 0.1);


const price = msrp * (1 - discount);
Asynchronous APIs

We mentioned earlier that after calling initialize most SDK APIs would run synchronously, so why are getConfig and checkGate asynchronous?

The main reason is that older versions of the SDK might not know how to interpret new types of gate conditions. In such cases the SDK will make an asynchronous call to our servers to fetch the result of a check. This can be resolved by upgrading the SDK, and we will warn you if this happens.

For more details, read our blog post about SDK evaluations. If you have any questions, please ask them in our Feedback Repository.

Step 5 - Log a custom event

Now that you have a Feature Gate or an Experiment set up, you may want to track some custom events and see how your new features or different experiment groups affect these events. This is super easy with Statsig - simply call the Log Event API and specify the user and event name to log; you additionally provide some value and/or an object of metadata to be logged together with the event:

statsig.logEvent(user, 'add_to_cart', 'SKU_12345', {'price': '9.99', 'item_name': 'diet_coke_48_pack'});

Statsig User

When calling APIs that require a user, you should pass as much information as possible in order to take advantage of advanced gate and config conditions (like country or OS/browser level checks), and correctly measure impact of your experiments on your metrics/events. The userID field is required because it's needed to provide a consistent experience for a given user (click here to understand further why it's important to always provide a userID).

Besides userID, we also have email, ip, userAgent, country, locale and appVersion as top-level fields on StatsigUser. In addition, you can pass any key-value pairs in an object/dictionary to the custom field and be able to create targeting based on them.

Have sensitive user PII data that should not be logged?

No problem, we have a solution for it! On the StatsigUser object we also have a field called privateAttributes, which is a simple object/dictionary that you can use to set private user attributes. Any attribute set in privateAttributes will only be used for evaluation/targeting, and removed from any logs before they are sent to Statsig server.

For example, if you have feature gates that should only pass for users with emails ending in "", but do not want to log your users' email addresses to Statsig, you can simply add the key-value pair { email: "" } to privateAttributes on the user and that's it!

Statsig Options

statsig.initialize() takes an optional parameter options in addition to the secret key that you can provide to customize the Statsig client. Here are the current options and we are always adding more to the list:

  • api: string, default

    • The base url to use for all network requests. Defaults to the statsig API.
  • environment: StatsigEnvironment, default null

    • An object you can use to set environment variables that apply to all of your users in the same session and will be used for targeting purposes.
    • The most common usage is to set the environment tier ('production', 'staging' or 'development'), e.g. { tier: 'staging' }, and have feature gates pass/fail for specific environments.
  • bootstrapValues: string, default null

    • a string that represents all rules for all feature gates, dynamic configs and experiments. It can be provided to bootstrap the Statsig server SDK at initialization in case your server runs into network issue or Statsig server is down temporarily.
  • rulesUpdatedCallback: function, default null

    • a callback function that's called whenever we have an update for the rules; it's called with a JSON string (used as is for bootstrapValues mentioned above) and a timestamp, like below:

      options.rulesUpdatedCallback(specsString, timeStamp)
  • localMode: boolean, default false

    • disables all network access, so the SDK will only return default (or overridden) values. Useful in testing
  • initTimeoutMs: number, default 0

    • sets a maximum time to wait for the config download network request to resolve before considering the SDK initialized and resolving the call to initialize()

Shutting down Statsig

Because we batch and periodically flush events, some events may not have been sent when your app/server shuts down. To make sure all logged events are properly flushed, you should tell Statsig to shutdown when your app/server is closing:


Alternatively, if you are operating in a serverless environment/cloud function, you may wish to leave Statsig running in case your function is recycled but flush the logs to Statsig servers. Or, if you need an async method to wait for logs to post before resolving, you can use:



Type StatsigUser

export type StatsigUser = {
userID: string;
email?: string;
ip?: string;
userAgent?: string;
country?: string;
locale?: string;
appVersion?: string;
custom?: Record<
string | number | boolean | Array<string> | undefined
privateAttributes?: Record<
string | number | boolean | Array<string> | undefined
customIDs?: Record<string, string>;

Type StatsigOptions

export type StatsigOptions = {
api?: string;
bootstrapValues?: string;
environment?: StatsigEnvironment;
localMode?: boolean;
rulesUpdatedCallback?: { (rulesJSON: string, time: number): void };
initTimeoutMs?: number;

Type StatsigEnvironment

export type StatsigEnvironment = {
tier?: "production" | "staging" | "development";
bootstrapValues: string;
rulesUpdatedCallback: function;


How do I run experiments for logged out users?

You can run experiments for arbitrary unit IDs (sessionID, groupID, etc), rather than at the userID level, if you choose. These custom unit IDs must be predefined in your Statsig project, and then selected in the Experiment creation flow. For more information, see our guide on experimenting on custom ID types

How can I use the node SDK for server side rendering?

The Node server SDK, starting in v4.13.0+ supports generating the initializeValues needed to bootstrap a statsig-js or statsig-react SDK and render it on the server/use the SDK without a round trip to Statsig servers.

const values = statsig.getClientInitializeResponse(user); // Record<string, unknown> | null
if (values != null) {
// boostrap your client SDK
return <StatsigSynchronousProvider initializeValues={values} ... />;

NOTE: This will not automatically use the ip, or userAgent for gate evaluation as statsig servers would, since there is no request from the client SDK specifying these values. If you want to use conditions like IP, or conditions which are inferred from the IP/UA like: Browser Name or Version, OS Name or Version, Country, you must manually set the ip and userAgent field on the user object when calling getClientInitializeResponse.

Similarly, there is no auto-generated stableID for device based experimentation, since the server generates the initialize response without any information from the client SDK. If you wish to run a device based experiment while using the server to generate the initialize resopnse, we recommend you:

  1. Create a customID in the Statsig console. See experimenting on custom IDs for more information.
  2. Generate an ID on the server, and set it in a cookie to be used on the client side as well.
  3. Set that ID as the customID on the StatsigUser object when generating the initialize response from the statsig-node sdk.
  4. Get that ID from the cookie, and set it as the customID on the StatsigUser object when using the client SDK, so all event data and exposure checks tie back to the same user.

Alternatively, if you wish to use the stableID field rather than a custom ID, you still need to do step (2) above. Then:

  • Set the stableID field on the StatsigUser object in the customIDs map when generating the initialize response from the statsig-node sdk
  • Override the stableID in the client SDK by getting the value from the cookie and setting the overrideStableID parameter in StatsigOptions

How can I mock Statsig for testing?

The Node server SDK, starting in version 4.8.0+, supports a few features to make testing easier.

First, there is a new StatsigOption paramter called localMode. Setting localMode to true will cause the SDK to never hit the network, and only return default values. This is perfect for dummy environments or test environments that should not access the network.

Next, there are the overrideGate and overrideConfig APIs on the global statsig instance:

function overrideGate(
gateName: string,
value: boolean,
userID?: string,
): void;
function overrideConfig(
gateName: string,
value: object,
userID?: string,
): void

These can be used to set a gate or config override for a specific user, or for all users (by not providing a specific user ID). Experiments/Autotune are overridden with the overrideConfig API.

We suggest you enable localMode and then override gates/configs/experiments to specific values to test the various code flows you are building.