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如何只将参数传递给需要它的中间件?

middleware express node.js javascript

Catfish · 技术社区 · 7 年前

我有一个Express应用程序,我正试图将我的所有中间件放在它自己的文件中。一些中间件功能需要 db 对象,有些则不然。

对于不需要 分贝 对象,但考虑到下面的代码结构,如何引用 分贝 中的对象 doesNotNeedDbParam 因为它已经有参数了 req , res 和 next ?

somefile.js文件:

const router = express.Router()
const doesNotNeedDbParam = require('./middleware')().doesNotNeedDbParam

function foo () {
  // Currently I have to call require and pass in the db object here b/c 
  // it's not set when requiring the function doesNotNeedDbParam
  router.use(require('./middleware')(db).needsDbParam // <-- Is there a better way to do this so that I can require the file above and pass the db object in when it's set?
}

// Setup db object here
foo()

中间件.js

function doesNotNeedDbParam (req, res, next) {
  ...
}

function needsDbParam (req, res, next) {
  // Where do I reference the db variable?
}

module.exports = (db) => {
  return {
    doesNotNeedDbParam: doesNotNeedDbParam,
    needsDbParam: needsDbParam
  }
}

2 回复 | 直到 7 年前

Andrew Li 7 年前

功能性方法

我认为一个好的结构是尝试 currying 你的中间件。这是由中间件(如 body-parser 内部通过表达自己 serve-static . 这样,你只需要一次,然后通过 db 你需要的地方,而不是你不需要的地方:

// Instead of declaring each function directly as a middleware function,
// we declare them as a function that returns a middleware function
function doesNotNeedDbParam () {
  return function (req, res, next) {
    â¦
  }
}

function needsDbParam (db) {
  return function (req, res, next) {
    // You can use db here along with req, res, next
  }
}

// No need to export a function now
module.exports = {
  doesNotNeedDbParam,
  needDbParam,
};

那么,只需要:

const middleware = require('./middleware');
â¦
router.use(middleware.doesNotNeedDbParam()); // Since this doesn't need anything, no argument
router.use(middleware.needsDbParam(db)); // You can pass db here now

如果您熟悉ES6+语法,可以将其浓缩为:

const doesNotNeedDbParam = () => (req, res, next) => {
  â¦
}

const needsDbParam = (db) => (req, res, next) => {
  // Use db here
}
// Export object here...

然后:

const { doesNotNeedDbParam, needsDbParam } = require('./middleware');
â¦ 
router.use(doesNotNeedDbParam());
router.use(needsDbParam(db));

附加进近

还有另一种方法可以做到这一点,将属性附加到 req 对象一旦 . 这样就不需要重新打包 分贝 每次你想要的时候。许多其他软件包使用这种策略。就像这样:

function attachDb (db) { // Still use curry approach here since we want db
  return function (req, res, next) {
    // Attaches the specified db to req directly
    req.db = db;
  }
}

function needsDbParam (req, res, next) { // No need for currying
  // Now use req.db here
}
// Export your other middlewareâ¦

然后,像这样使用,确保 attachDb 是第一以便在使用该属性之前对其进行分配:

router.use(attachDb(db)); // Before all other middleware that depend on req.db
â¦
// No need to call because this is already the middleware function, 
// able to use req.db, which was assigned via attachDb
router.use(needDbParam);

-1

NoxelNyx 7 年前

为什么不直接申报呢 module.exports 作为单一功能:

module.exports = (db) => { 
    let module = {}; 

    module.doesNotNeedDbParam = (req, res) => {
        // Do Stuff
    };

    module.needsDbParam = (req, res) => { 
        // db now in scope
    };

    return module;
};

这就是你的 somefile.js 会变成:

const router = express.Router();
const db = initializeDb();

const doesNotNeedDbParam = require('./middleware')().doesNotNeedDbParam;
router.use(require('./middleware')(db).needsDbParam);

您也可以这样设置它:

const middleware = require('./middleware')(db);
const doesNotNeedParam = middleware.doesNotNeedParam;
router.use(middleware.needsDbParam);

这与您以前所做的没有什么不同,但现在您可以访问 needsDbParam . 如果你的 initializeDb 函数是异步的,则需要使用 Promise 或者在数据库建立之后要包含的其他异步库。