Edit

JavaScript (SSR)

For Server-Side Rendered JavaScript frameworks like NuxtJS

Getting started

1. Install and import package

via NPM:

npm i configcat-js-ssr

import * as configcat from "configcat-js-ssr";

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();
    }
});

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
sdkKey	REQUIRED. SDK 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
);

or

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"
};   

or

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(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

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

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 setting values are 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

let 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.

let 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":"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-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.

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

Sample Applications

• NuxtJS

Look under the hood

• ConfigCat JavaScript (SSR) SDK on GitHub
• ConfigCat JavaScript (SSR) SDK in NPM