JavaScript

For JavaScript SSR (Server-Side Rendered) applications we recommend using ConfigCat JS-SSR SDK

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/[email protected]/dist/configcat.min.js"></script>

2. Create the ConfigCatClient with your SDK Key:

var configCatClient = configcat.createClient("#YOUR-SDK-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

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(sdkKey, options) returns a client with default options.

Properties	Description	Default
`sdkKey`	REQUIRED. SDK Key to access your feature flags and configurations. Get it from ConfigCat Dashboard.	-
`options`	Optional. More about the options parameter.	-

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

caution

We strongly recommend you to use the ConfigCat Client as a Singleton object in your application. If you want to use multiple SDK Keys in the same application, create only one ConfigCat Client per SDK Key.

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 : "[email protected]"
};

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 : "[email protected]",
    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 getValue() calls 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(sdkKey, 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
`dataGovernance`	Describes the location of your feature flag and setting data within the ConfigCat CDN. This parameter needs to be in sync with your Data Governance preferences. More about Data Governance. Available options: `Global`, `EuOnly`.	`Global`
`maxInitWaitTimeSeconds`	Maximum waiting time between the client initialization and the first config acquisition in seconds.	5

Use the pollIntervalSeconds option parameter to change the polling interval.

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

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

configcat.createClientWithAutoPoll("#YOUR-SDK-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(sdkKey, 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
`dataGovernance`	Describes the location of your feature flag and setting data within the ConfigCat CDN. This parameter needs to be in sync with your Data Governance preferences. More about Data Governance. Available options: `Global`, `EuOnly`.	`Global`

Use cacheTimeToLiveSeconds option parameter to set cache lifetime.

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

Manual polling

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

`createClientWithManualPoll(sdkKey, 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
`dataGovernance`	Describes the location of your feature flag and setting data within the ConfigCat CDN. This parameter needs to be in sync with your Data Governance preferences. More about Data Governance. Available options: `Global`, `EuOnly`.	`Global`

const configCatClient = configcat.createClientWithManualPoll("#YOUR-SDK-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.

const configCatClient = configcat.createClientWithManualPoll("#YOUR-SDK-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-SDK-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":"[email protected]"}
 Evaluating rule: '[email protected]' CONTAINS '@something.com' => no match
 Evaluating rule: '[email protected]' CONTAINS '@example.com' => MATCH
 Returning value : true

`getAllKeys()`

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

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

`getAllKeysAsync()`

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

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

`getAllValues()`

Evaluates and returns the values of all feature flags and settings. Passing a User Object is optional.

const configCatClient = configcat.createClient("#YOUR-SDK-KEY#");
configCatClient.getAllValues(function(settingValues) {
    settingValues.forEach(i => console.log(i.settingKey + ' -> ' + i.settingValue));
});


// invoke with user object
const userObject = {
    identifier : "[email protected]"
}; 

configCatClient.getAllValues(function(settingValues) {
    settingValues.forEach(i => console.log(i.settingKey + ' -> ' + i.settingValue));
}, userObject);

`getAllValuesAsync()`

Evaluates and returns the values of all feature flags and settings. Passing a User Object is optional.

const configCatClient = configcat.createClient("#YOUR-SDK-KEY#");
const settingValues = await configCatClient.getAllValuesAsync();
settingValues.forEach(i => console.log(i.settingKey + ' -> ' + i.settingValue));

// invoke with user object
const userObject = {
    identifier : "[email protected]"
}; 

const settingValuesTargeting = await configCatClient.getAllValuesAsync(userObject);
settingValuesTargeting.forEach(i => console.log(i.settingKey + ' -> ' + i.settingValue));

JavaScript

Getting started

1. Install and import package

2. Create the ConfigCatClient with your SDK Key:

3. Get your setting value:

Working Demo on CodePen

Creating the ConfigCat Client

caution

Anatomy of `getValue()`

`getValueAsync()`

User Object

Polling Modes

Auto polling (default)

`createClientWithAutoPoll(sdkKey, options)`

Lazy loading

`createClientWithLazyLoad(sdkKey, options)`

Manual polling

`createClientWithManualPoll(sdkKey, options)`

Logging

Setting log levels

`getAllKeys()`

`getAllKeysAsync()`

`getAllValues()`

`getAllValuesAsync()`

Sample Applications

Look under the hood

Getting started​

1. Install and import package​

2. Create the ConfigCatClient with your SDK Key:​

3. Get your setting value:​

Working Demo on CodePen​

Creating the ConfigCat Client​

caution

Anatomy of getValue()​

getValueAsync()​

User Object​

Polling Modes​

Auto polling (default)​

createClientWithAutoPoll(sdkKey, options)​

Lazy loading​

createClientWithLazyLoad(sdkKey, options)​

Manual polling​

createClientWithManualPoll(sdkKey, options)​

Logging​

Setting log levels​

getAllKeys()​

getAllKeysAsync()​

getAllValues()​

getAllValuesAsync()​

Sample Applications​

Look under the hood​

Getting started

1. Install and import package

2. Create the ConfigCatClient with your SDK 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(sdkKey, options)`

Lazy loading

`createClientWithLazyLoad(sdkKey, options)`

Manual polling

`createClientWithManualPoll(sdkKey, options)`

Logging

Setting log levels

`getAllKeys()`

`getAllKeysAsync()`

`getAllValues()`

`getAllValuesAsync()`

Sample Applications

Look under the hood