Express 应用程序的 Route.get() 需要回调函数，但出现 [object Undefined] 错误

Question

I have the following health.js file..

var health = function(req, res, done) {};
health.prototype.endpoint = function(req, res, done) {
    let http_status = 200;
    console.log("--- Sending health endpoint status of %s", http_status);
    res.sendStatus(http_status);
    done();
};

module.exports = health;

Which is being called in routes.js

module.exports = function (app) {
    let index = require('./endpoints/helloworld'),
        health = require('./endpoints/health').endpoint,
        metadata = require('./endpoints/metadata');

    app.get('/', index.endpoint);
    app.get('/health', health);
    app.get('/metadata', metadata.endpoint);
};

But when I try to run my app, I receive the following error..

Attaching to myapp_app_1
app_1  | npm info it worked if it ends with ok
app_1  | npm info using npm@3.10.10
app_1  | npm info using node@v6.11.4
app_1  | npm info lifecycle my-app@1.0.0~prestart-local: my-app@1.0.0
app_1  | npm info lifecycle my-app@1.0.0~start-local: my-app@1.0.0
app_1  |
app_1  | > my-app@1.0.0 start-local /app
app_1  | > node ./src/index.js
app_1  |
app_1  | /app/node_modules/express/lib/router/route.js:202
app_1  |         throw new Error(msg);
app_1  |         ^
app_1  |
app_1  | Error: Route.get() requires a callback function but got a [object Undefined]
app_1  |     at Route.(anonymous function) [as get] (/app/node_modules/express/lib/router/route.js:202:15)
app_1  |     at EventEmitter.app.(anonymous function) [as get] (/app/node_modules/express/lib/application.js:482:19)
app_1  |     at module.exports (/app/src/routes.js:10:9)
app_1  |     at Object.<anonymous> (/app/src/index.js:12:20)
app_1  |     at Module._compile (module.js:570:32)
app_1  |     at Object.Module._extensions..js (module.js:579:10)
app_1  |     at Module.load (module.js:487:32)
app_1  |     at tryModuleLoad (module.js:446:12)
app_1  |     at Function.Module._load (module.js:438:3)
app_1  |     at Module.runMain (module.js:604:10)
app_1  |
app_1  | npm info lifecycle my-app@1.0.0~start-local: Failed to exec start-local script
app_1  | npm ERR! Linux 4.9.49-moby
app_1  | npm ERR! argv "/usr/local/bin/node" "/usr/local/bin/npm" "run" "start-local"
app_1  | npm ERR! node v6.11.4
app_1  | npm ERR! npm  v3.10.10
app_1  | npm ERR! code ELIFECYCLE
app_1  | npm ERR! my-app@1.0.0 start-local: `node ./src/index.js`
app_1  | npm ERR! Exit status 1
app_1  | npm ERR!
app_1  | npm ERR! Failed at the my-app@1.0.0 start-local script 'node ./src/index.js'.
app_1  | npm ERR! Make sure you have the latest version of node.js and npm installed.
app_1  | npm ERR! If you do, this is most likely a problem with the my-app package,
app_1  | npm ERR! not with npm itself.
app_1  | npm ERR! Tell the author that this fails on your system:
app_1  | npm ERR!     node ./src/index.js
app_1  | npm ERR! You can get information on how to open an issue for this project with:
app_1  | npm ERR!     npm bugs my-app
app_1  | npm ERR! Or if that isn't available, you can get their info via:
app_1  | npm ERR!     npm owner ls my-app
app_1  | npm ERR! There is likely additional logging output above.
app_1  | npm ERR! Linux 4.9.49-moby
app_1  | npm ERR! argv "/usr/local/bin/node" "/usr/local/bin/npm" "run" "start-local"
app_1  | npm ERR! node v6.11.4
app_1  | npm ERR! npm  v3.10.10
app_1  | npm ERR! path npm-debug.log.896050243
app_1  | npm ERR! code EACCES
app_1  | npm ERR! errno -13
app_1  | npm ERR! syscall open
app_1  |
app_1  | npm ERR! Error: EACCES: permission denied, open 'npm-debug.log.896050243'
app_1  | npm ERR!     at Error (native)
app_1  | npm ERR!  { Error: EACCES: permission denied, open 'npm-debug.log.896050243'
app_1  | npm ERR!     at Error (native)
app_1  | npm ERR!   errno: -13,
app_1  | npm ERR!   code: 'EACCES',
app_1  | npm ERR!   syscall: 'open',
app_1  | npm ERR!   path: 'npm-debug.log.896050243' }
app_1  | npm ERR!
app_1  | npm ERR! Please try running this command again as root/Administrator.
app_1  |
app_1  | npm ERR! Please include the following file with any support request:
app_1  | npm ERR!     /app/npm-debug.log

Why am I receiving this error?

Answer 1

I'm not really clear what you're trying to do but I can explain why you're seeing that error.

Here are the relevant bits of health.js :

var health = function(req, res, done) {};

health.prototype.endpoint = function(req, res, done) {
   ...
};

module.exports = health;

So you've got an empty function called health and then you've added something to it's prototype. Adding something to the prototype is a bit strange unless you're planning to create an instance of health , like this:

var myHealth = new health();
var endpoint = health.endpoint;

It seems unlikely that's what you had in mind.

In your routes.js you've got this:

health = require('./endpoints/health').endpoint,

The variable health will be undefined because there is no endpoint property for the exported function. You could fix it by whacking in prototype but again I don't think it's really what you want:

health = require('./endpoints/health').prototype.endpoint,

If that empty health function needs to be maintained as the thing that gets exported then you could just get rid of the word prototype in health.js :

health.endpoint = function(req, res, done) {
    ...
};

However if you don't need that empty function and just want to export something called endpoint you could change health.js to something like this:

exports.endpoint = function(req, res, done) {
    ...
};

Answer 2

 health = require('./endpoints/health').endpoint,

尝试将健康作为一个模块，比如{health}

Answer 3

You have not posted the entire error. So that we can find the line number of error. But express usually throws this error if the callback provide to its route doesn't resolve to a function or is undefined. You can recheck if you have given correct path for each route.