Edit

JavaScript

Getting started

1. Install and import package

via NPM:

npm i configcat-js

import * as configcat from "configcat-js";

via CDN:

<script type="text/javascript" src="https://cdn.jsdelivr.net/npm/configcat-js@latest/dist/configcat.min.js"></script>

2. Create the ConfigCatClient with your API Key:

var configCatClient = configcat.createClient("#YOUR-API-KEY#");

3. Get your setting value:

configCatClient.getValue("isMyAwesomeFeatureEnabled", false, function(value) {
    if(value) {
        do_the_new_thing();
    } else {
        do_the_old_thing();
    }
});

Working Demo on CodePen

See the Pen ConfigCat feature flags based dynamically updating page by ConfigCat (@configcat) on CodePen.

Creating the ConfigCat Client

ConfigCat Client is responsible for:

• managing the communication between your application and ConfigCat servers.
• caching your setting values and feature flags.
• serving values quickly in a failsafe way.

createClient() returns a client with default options.

Properties	Description
apiKey	REQUIRED. API Key to access your feature flags and configurations. Get it from ConfigCat Management Console.

createClientWithAutoPoll(), createClientWithLazyLoad(), createClientWithManualPoll()
Creating the client is different for each polling mode. See below for details.

We strongly recommend using the ConfigCat Client as a Singleton object in your application.

Anatomy of getValue()

Parameters	Description
key	REQUIRED. Setting-specific key. Set in ConfigCat Management Console for each setting.
defaultValue	REQUIRED. This value will be returned in case of an error.
callback	REQUIRED. Called with the actual setting value.
user	Optional, User Object. Essential when using Targeting. Read more about Targeting.

configCatClient.getValue(
    "keyOfMySetting", // Setting Key
    false, // Default value
    function(value) { console.log(value) }, // Callback function
    { identifier : "435170f4-8a8b-4b67-a723-505ac7cdea92" } // Optional User Object
);

User Object

var userObject = {
    identifier : "435170f4-8a8b-4b67-a723-505ac7cdea92"
};   

var userObject = {
    identifier : "john@example.com"
};   

Parameters	Description
identifier	REQUIRED. Unique identifier of a user in your application. Can be any string value, even an email address.
email	Optional parameter for easier targeting rule definitions.
country	Optional parameter for easier targeting rule definitions.
custom	Optional dictionary for custom attributes of a user for advanced targeting rule definitions. e.g. User role, Subscription type.

var userObject = {
    identifier : "435170f4-8a8b-4b67-a723-505ac7cdea92",
    email : "john@example.com",
    country : "United Kingdom",
    custom : {
        "SubscriptionType": "Pro",
        "UserRole": "Admin"
    }
};

Polling Modes

The ConfigCat SDK supports 3 different polling mechanisms to acquire the setting values from ConfigCat. After latest setting values are downloaded, they are stored in the internal cache then all requests are served from there. With the following polling modes, you can customize the SDK to best fit to your application's lifecycle.

Auto polling (default)

The ConfigCat SDK downloads the latest values and stores them automatically every 60 seconds.

Use the pollIntervalSeconds option parameter to change the polling interval.

configcat.createClientWithAutoPoll("#YOUR-API-KEY#", { pollIntervalSeconds: 95 });

Adding a callback to configChanged option parameter will get you notified about changes.

configcat.createClientWithAutoPoll("#YOUR-API-KEY#", { configChanged: function() {
    console.log("Your config has been changed!");
}});

Available options:

Option Parameter	Description	Default
pollIntervalSeconds	Polling interval. Range: 1 - Number.MAX_SAFE_INTEGER	60
configChanged	Callback to get notified about changes.	-
logger	Custom logger. See below for details.	Console logger

Lazy loading

When calling getValue() the ConfigCat SDK downloads the latest setting values if they are not present or expired in the cache. In this case the callback will be called after the cache is updated.

Use cacheTimeToLiveSeconds option parameter to set cache lifetime.

configcat.createClientWithLazyLoad("#YOUR-API-KEY#", { cacheTimeToLiveSeconds: 600 });

Available options:

Option Parameter	Description	Default
cacheTimeToLiveSeconds	Cache TTL. Range: 1 - Number.MAX_SAFE_INTEGER	60
logger	Custom logger.

Manual polling

Manual polling gives you full control over when the setting values are downloaded. ConfigCat SDK will not update them automatically. Calling forceRefresh() is your application's responsibility.

let configCatClient = configcat.createClientWithManualPoll("#YOUR-API-KEY#");

configCatClient.forceRefresh(() =>{

    configCatClient.getValue("key", "my default value", (value)=>{
        
        console.log(value);
    });
});

Available options:

Option Parameter	Description	Default
logger	Custom logger. See below for details.	Console logger

getValue() returns defaultValue if the cache is empty. Call forceRefresh() to update the cache.

let configCatClient = configcat.createClientWithManualPoll("#YOUR-API-KEY#");

configCatClient.getValue("key", "my default value", (value)=>{

    console.log(value) // console: "my default value"
});

configCatClient.forceRefresh(() =>{

    configCatClient.getValue("key", "my default value", (value)=>{

        console.log(value); // console: "value from server"
    });
});

Logging

To customize logging create a logger instance and add it to Options object when creating the ConfigCat client. 2 log levels are supported: log and error.

var customLogger = {
    log: function(message) {
        console.log('ConfigCat log: ' + message);
    },
    error: function(message) {
        console.error('ConfigCat log: ' + message);
    }
};

configcat.createClientWithManualPoll("#YOUR-API-KEY#", { logger: customLogger });

CDN base url (forward proxy, dedicated subscription)

You can customize your CDN path in the SDK with baseUrl property in the options parameter.

var configCatClient = configcat.createClientWithManualPoll("#YOUR-API-KEY#", { baseUrl: "https://myCDN.configcat.com" });

getAllKeys()

You can query the keys from your config file in the SDK with the getAllKeys() method.

var configCatClient = configcat.createClient("#YOUR-API-KEY#");
configCatClient.getAllKeys(function(keys) {
    console.log(keys);
});

Sample Applications

• Angular 2+
• React
• Pure HTML + JS

Look under the hood

• ConfigCat's JavaScript SDK on GitHub
• ConfigCat JavaScript SDK in NPM