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Neff is simple express middleware for handling feature flags.


The standard way to use neff on the client & the server side is to check for enabled features using the isEnabled() API.

var users = 500;
var moreUsers = neff.isEnabled("moreUsers");
if (moreUsers) {

Argument-Based Config

To get started with neff you'll want to make sure you call neff, passing it an an object with feature names and either true or false values.

var neff = require("neff")({
    "feature1": true,
    "feature2": false

NConf-Based Config

If you'd like to utilize NConf for this, you can reference an NConf JSON file and my config looks like this:

    "feature1": true,
    "feature2": false

Then pass the config object for the features to neff:

var neff = require("neff")(nconf.get('features'));

Accessing in templates

The first thing it allows you to do is access feature flags directly in your template such as (dust syntax):


Express Router Limiter

This route is only available when the feature flag is enabled. Otherwise the user would see a server error page.

var neff = require("neff");
app.get("/myhidden/route", neff.limit("feature1"), function(req, res) {
   res.send("You have found feature1!");

Client Side Usage

It also provides a string of class names you can insert into your <body> (dust syntax):

<body class="{featureClasses}">

The output prepends feature- to the classname, so you might see something like <body class="feature-feature1"> with the config above. Only enabled features show up in the string.

Make sure your features are declared on your DOM like so:

<body class="feature-feature1 feature-feature2">

Once you've done that you can take advantage of the flags in 2 ways.


/* Create a block that's hidden by default */
.my-cool-block {
    display: none;
/* Display that block when your flag is present */
.feature-feature1 .my-cool-block {
    display: block;


define(["neff"], function(neff) {
    if (neff.isEnabled("feature1")) {
        /* .. */


Inspired heavily by