JavaScript

For SSR (Server-Side Rendering) Universal applications we recommend using ConfigCat SDK for Node.js

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:

The Promise (async/await) way:

configCatClient.getValueAsync("isMyAwesomeFeatureEnabled", false)
.then((value) => {
    if(value) {
        do_the_new_thing();
    } else {
        do_the_old_thing();
    }
});

or the Callback way:

configCatClient.getValue("isMyAwesomeFeatureEnabled", false, (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 Dashboard.

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 on ConfigCat Dashboard 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
);

`getValueAsync()`

Returns a Promise with the value.

Parameters	Description
`key`	REQUIRED. Setting-specific key. Set on ConfigCat Dashboard for each setting.
`defaultValue`	REQUIRED. This value will be returned in case of an error.
`user`	Optional, User Object. Essential when using Targeting. Read more about Targeting.

const value = await configCatClient.getValueAsync(
    "keyOfMySetting", // Setting Key
    false, // Default value
    { identifier : "435170f4-8a8b-4b67-a723-505ac7cdea92" } // Optional User Object
);

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

User Object

The User Object is essential if you'd like to use ConfigCat's Targeting feature. For simple targeting:

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.

For advanced targeting:

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.

`createClientWithAutoPoll(apiKey, 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
`requestTimeoutMs`	The amount of milliseconds the SDK waits for a response from the ConfigCat servers before returning values from the cache.	30000

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!");
}});

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.

`createClientWithLazyLoad(apiKey, options)`

Option Parameter	Description	Default
`cacheTimeToLiveSeconds`	Cache TTL. Range: `1 - Number.MAX_SAFE_INTEGER`	60
`logger`	Custom logger. See below for details.	Console logger
`requestTimeoutMs`	The amount of milliseconds the SDK waits for a response from the ConfigCat servers before returning values from the cache.	30000

Use cacheTimeToLiveSeconds option parameter to set cache lifetime.

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

Manual polling

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

`createClientWithManualPoll(apiKey, options)`

Option Parameter	Description	Default
`logger`	Custom logger. See below for details.	Console logger
`requestTimeoutMs`	The amount of milliseconds the SDK waits for a response from the ConfigCat servers before returning values from the cache.	30000

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

configCatClient.forceRefresh(() =>{

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

getValue() returns defaultValue if the cache is empty. Call forceRefresh() or forceRefreshAsync() 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

Setting log levels

const logger = configcat.createConsoleLogger(3); // Setting log level to 3 (= Info)

const configCatClient = configcat.createClientWithAutoPoll('#YOUR-API-KEY#', 
    { logger: logger }
);

Available log levels:

Level	Name	Description
-1	Off	Nothing gets logged.
1	Error	Only error level events are logged.
2	Warn	Errors and Warnings are logged.
3	Info	Errors, Warnings and feature flag evaluation is logged.

Info level logging helps to inspect the feature flag evaluation process:

ConfigCat - INFO - Evaluate 'isPOCFeatureEnabled'
 User : {"identifier":"#SOME-USER-ID#","email":"configcat@example.com"}
 Evaluating rule: 'configcat@example.com' CONTAINS '@something.com' => no match
 Evaluating rule: 'configcat@example.com' CONTAINS '@example.com' => MATCH
 Returning value : true

`getAllKeys()`

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

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

`getAllKeysAsync()`

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

let configCatClient = configcat.createClient("#YOUR-API-KEY#");
const keys = await configCatClient.getAllKeysAsync();
console.log(keys);

ConfigCat Docs

Getting started

1. Install and import package

2. Create the ConfigCatClient with your API Key:

3. Get your setting value:

Working Demo on CodePen

Creating the ConfigCat Client

Anatomy of `getValue()`

`getValueAsync()`

User Object

Polling Modes

Auto polling (default)

`createClientWithAutoPoll(apiKey, options)`

Lazy loading

`createClientWithLazyLoad(apiKey, options)`

Manual polling

`createClientWithManualPoll(apiKey, options)`

Logging

Setting log levels

`getAllKeys()`

`getAllKeysAsync()`

Sample Applications

Look under the hood

Getting started

1. Install and import package

2. Create the ConfigCatClient with your API Key:

3. Get your setting value:

Working Demo on CodePen

Creating the ConfigCat Client

Anatomy of getValue()

getValueAsync()

User Object

Polling Modes

Auto polling (default)

createClientWithAutoPoll(apiKey, options)

Lazy loading

createClientWithLazyLoad(apiKey, options)

Manual polling

createClientWithManualPoll(apiKey, options)

Logging

Setting log levels

getAllKeys()

getAllKeysAsync()

Sample Applications

Look under the hood

Anatomy of `getValue()`

`getValueAsync()`

`createClientWithAutoPoll(apiKey, options)`

`createClientWithLazyLoad(apiKey, options)`

`createClientWithManualPoll(apiKey, options)`

`getAllKeys()`

`getAllKeysAsync()`