Example

## Basic

We define a Person class.
// the target object
class Person {
  // the target function
  walk(step) {
    this.step = step;
  }

  speak(word) {
    this.word = word;
  }
}

Then we define a middleware function to print log.

// middleware for walk function
const logger = target => next => (...args) => {
  console.log(`walk start, steps: ${args[0]}.`);
  const result = next(...args);
  console.log(`walk end.`);
  return result;
}

Now we apply the log function as a middleware to a Person instance.

// apply middleware to target object
const p = new Person();
const middlewareManager = new MiddlewareManager(p);
middlewareManager.use('walk', logger);
p.walk(3);

Whenever a Person instance call it's walk method, we'll see logs from the looger middleware.

## Middleware object
We can also apply a middleware object to a target object.
Middleware object is an object that contains function's name as same as the target object's function name.

const PersonMiddleware = {
  walk: target => next => step => {
    console.log(`walk start, steps: step.`);
    const result = next(step);
    console.log(`walk end.`);
    return result;
  },
  speak: target => next => word => {
    word = 'this is a middleware trying to say: ' + word;
    return next(word);
  }
}

// apply middleware to target object
const p = new Person();
const middlewareManager = new MiddlewareManager(p);
middlewareManager.use(PersonMiddleware);
p.walk(3);
p.speak('hi');

## middlewareMethods
In a class, function's name start or end with "_" will not be able to apply as middleware.
Or we can use `middlewareMethods` to define function names for middleware target within a class.

class PersonMiddleware {
  constructor() {
    // Or Define function names for middleware target.
    this.middlewareMethods = ['walk', 'speak'];
  }
  // Function's name start or end with "_" will not be able to apply as middleware.
  _getPrefix() {
    return 'Middleware log: ';
  }
  log(text) {
    console.log(this._getPrefix() + text);
  }
  walk(target) {
    return next => step => {
      this.log(`walk start, steps: step.`);
      const result = next(step);
      this.log(`walk end.`);
      return result;
    }
  }
  speak(target) {
    return next => word => {
      this.log('this is a middleware trying to say: ' + word);
      return next(word);
    }
  }
}

// apply middleware to target object
const p = new Person();
const middlewareManager = new MiddlewareManager(p);
middlewareManager.use(new PersonMiddleware())
p.walk(3);
p.speak('hi');

Parameters:

Returns:

Type

object