apply-middleware

Apply any number of middleware functions to the target function. Created with ds-library-starter.

Installation

npm:

npm install apply-middleware

yarn:

yarn add apply-middleware

Usage

The applyMiddleware() function takes the list of functions as arguments.

The first function represents the target function, and every next function represents the middleware function.

applyMiddleware(targetFunction, middleware1, middleware2, ...middlewares);

Middleware function

The first argument of the middleware function is the next() callback.

Invoking the next() callback will invoke the next() middleware in the list.

In the last middleware function, the next() callback will invoke the target function.

function myMiddleware (next, ...arguments) {
   next();
}

If we pass the arguments to the next() callback, they will be passed to the next middleware function replacing the previous arguments.

function myMiddleware (next, ...arguments) {
   const newArguments = arguments.map(arg => arg + 1);
   next(newArguments);
}

If no arguments are passed to the next() callback, the next middleware will receive the same, unchanged arguments as the current middleware.

Example

import applyMiddleware from 'apply-middleware';

function addTimestamp (next, ...args) {
   const timestamp = new Date().toUTCString();
   next(timestamp, '---', ...args);
};

console.log = applyMiddleware(console.log, addTimestamp);

console.log('Hello', 'World'); // Sat, 30 Nov 2019 23:53:56 GMT --- Hello World

Another example

import applyMiddleware from 'apply-middleware';

function addOne (next, a, b) {
   next(a + 1, b + 1);
});

function logNumbers (next, a, b) {
   console.log(a, b);
   next();
});

function addDecimal (next, a, b) {
   next(a + 0.1, b + 0.1);
});

function saveToLocalStorage (a, b) {
   const json = JSON.stringify({ a, b });
   localStorage.setItem('numbers', json);
   console.log('Numbers have been saved to the local storage');
}

const withMiddleware = applyMiddleware(
   // Function to be wrapped
   saveToLocalStorage,

   // List of middlewares
   logNumbers,
   addOne,
   logNumbers,
   addDecimal,
   logNumbers
)

withMiddleware(1, 11);

// Execution order 
// logNumbers / console = 1, 11
// addOne
// logNumbers / console = 2, 13
// addDecimal
// logNumbers / console = 2.0, 13.0
// saveToLocalStorage / console = Numbers have been saved to the local storage