keep-or-skip

Dynamically execute or skip express middlewares

This wrapper allows you to choose one or more middlewares whose execution is based on a certain condition. The aforementioned condition could be, for instance, a specific request value.

Installation

npm i keep-or-skip --save

API

keepOrSkip(middlewares, predicate[, debug])

• middlewares <Function> | <Function[]> A middleware or an array of middlewares to be handled dynamically.
• predicate <Function> A function returning a boolean value affecting the execution of the speciefied middlewares. This function takes as input two optional parameters, the request and the response objects. If the predicate does not return a boolean value, middlewares will be skipped.
• debug <Boolean> An optional boolean parameter enabling a warning log which notifies whether predicate returned a boolean value. Default: false.
• returns An array of middlewares.

If the parameters' type does not match with those required, an error will be thrown. In pariticular, the error will be an instance of KeepOrSkipError.

Example

Consider the following example:

const express = require('express')
const keepOrSkip = require('keep-or-skip')

const app = express()

function setValue(req, res, next) {
    req.value = 1
    next()
}

function middlewareOne(req, res, next) {
    req.message = 'Hi from middlewareOne'
    next()
}

function middlewareTwo(req, res, next) {
    req.message = 'Hi from middlewareTwo'
    next()
}

function respond(req, res, next) {
    res.status(200).json({
        message: req.message
    })
}

const maybeMiddlewareOne = keepOrSkip(middlewareOne, req => req.value < 0)
const maybeMiddlewareTwo = keepOrSkip(middlewareTwo, req => req.value >= 0)

app.get('/',
    setValue,
    maybeMiddlewareOne,
    maybeMiddlewareTwo,
    respond
)

app.listen(3000)

http://localhost:3000 will produce the following result, middlewareOne is skipped and middlewareTwo is executed:

{
    "message": "Hi from middlewareTwo"
}

Debug

In case predicate does not return a boolean value, middlewares will be skipped. In this situation it's possible to log a warning by using the debug mode.

It's possible to activate the debug globally, directly on the imported module:

const keepOrSkip = require('keep-or-skip')
keepOrSkip.debug(true)

the above code sets the debug mode to true every time keepOrSkip is used unless otherwise specified in the single calls as shown in the following example:

const keepOrSkip = require('keep-or-skip')

// Set debug mode globally.
keepOrSkip.debug(true)

// Specifying the debug parameter at the time of use will overwrite the global debug variable.
keepOrSkip(myMiddlewares, myPredicate, false) // Debug OFF.

keepOrSkip(myMiddlewares, myPredicate) // Debug ON because of the global debug variable.