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用 MiddlewareJS 开始中间件编程,让代码和 ExpressJS, ReduxJS 一样容易扩展

ExpressJS 和 ReduxJS 的易扩展性正是得益于应用了中间件的设计模式。如果想在自己平日的项目里使用,可以试试 Middleware.js 这个中间件工具,它能使任意对象中间件化,用好中间件能有效解藕代码也易于维护。

MiddlewareJS 已发布到GitHub

Readme

Apply middleweare to an object.

Middleware functions are functions that have access to the target function and it's arguments, and the target object and the next middleware function in the target function cycle. The next middleware function is commonly denoted by a variable named next.

Middleware functions can perform the following tasks:

  • Execute any code.
  • Make changes to the function's arguments.
  • End the target function.
  • Call the next middleware in the stack.

    If the current middleware function does not end the target function cycle, it must call next() to pass control to the next middleware function. Otherwise, the target function will be left hanging.

API

.use(methodName, ...middlewares)

Apply middleware to the target object.

  • {string|object} methodName String for target function name, object
  • {...function} middlewares The middleware chain to be applied.
  • return {object} this

Usages

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 applyMiddleware = new ApplyMiddleware(p);
 applyMiddleware.use('walk', walk);
 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. Function's name start or end with "_" will not be able to apply middleware.

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 applyMiddleware = new ApplyMiddleware(p);
applyMiddleware.use(PersonMiddleware);
 p.walk(3);
 p.speak('hi');

middlewareMethods

Or we can use middlewareMethods to define function names for middleweare target within a class.

class CuePointMiddleware {
  constructor() {
    /**
     * Define function names for middleweare target.
     * @type {Array}
     */
    this.middlewareMethods = ['walk', 'speak'];
  }
  log(text) {
    console.log('Middleware log: ' + 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 tring to say: ' + word);
      return next(word);
    }
  }
}

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