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0.0.60 • Public • Published

Bullet Train Client

npm version

The SDK clients for web and React Native for Bullet Train allows you to manage feature flags and remote config across multiple projects, environments and organisations.

Getting Started

For full documentation visit

These instructions will get you a copy of the project up and running on your local machine for development and testing purposes. See running in production for notes on how to deploy the project on a live system.


npm i bullet-train-client --save

Retrieving feature flags for your project

import bulletTrain from "bullet-train-client"; //Add this line if you're using bulletTrain via npm
    onChange: (oldFlags,params)=>{ //Occurs whenever flags are changed
        const {isFromServer} = params; //determines if the update came from the server or local cached storage
        //Check for a feature
        if (bulletTrain.hasFeature("myCoolFeature")){
        //Or, use the value of a feature
        const bannerSize = bulletTrain.getValue("bannerSize");
        //Check whether value has changed
        const bannerSizeOld = oldFlags["bannerSize"] && oldFlags["bannerSize"].value;
        if (bannerSize !== bannerSizeOld) {

Initialisation options

Property Description Required Default Value
environmentID Defines which project environment you wish to get flags for. example ACME Project - Staging. YES null
onChange Your callback function for when the flags are retrieved (flags,{isFromServer:true/false})=>{...} YES null
onError Callback function on failure to retrieve flags. (error)=>{...} null
defaultFlags Allows you define default features, these will all be overridden on first retrieval of features. null
disableCache If you want to disable local storage of feature flags. false
api Use this property to define where you're getting feature flags from, e.g. if you're self hosting.

Available Functions

Property Description
init Initialise the sdk against a particular environment
hasFeature(key) Get the value of a particular feature e.g. bulletTrain.hasFeature("powerUserFeature") // true
getValue(key) Get the value of a particular feature e.g. bulletTrain.getValue("font_size") // 10
startListening(ticks=1000) Poll the api for changes every x milliseconds
stopListening() Stop polling the api
getFlags() Trigger a manual fetch of the environment features, if a user is identified it will fetch their features
identify(userId) Identify as a user, this will create a user for your environment in the dashboard if they don't exist, it will also trigger a call to getFlags()
getTrait(key) Get a user trait (e.g. favourite_colour), traits come back with getFlags(). I.e. as soon as a identify, setTrait and incrementTrait are called.
setTrait(key, value) Set a trait value for the currently identified user, it will also trigger a call to getFlags()
incrementTrait(key, amount) Increment a trait value for the currently identified user (accepts positive and negative values), it will also trigger a call to getFlags()
logout() Stop identifying as a user, this will trigger a call to getFlags()


Please read for details on our code of conduct, and the process for submitting pull requests to us.

Getting Help

If you encounter a bug or feature request we would like to hear about it. Before you submit an issue please search existing issues in order to prevent duplicates.

Get in touch

If you have any questions about our projects you can email


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