ExpressJS-路由功能

Question

I created a separate JS file for specific server functions. Sample code as follow:

my-data.js

var exports = module.exports = {};
exports.getData = function (request, response) {
    var myData = [
        {
            "value": 1
        },
        {
            "value": 2
        },
    ];
    response.json(myData);
};

In my app.js , I'm trying to call that specific function when the request has been made.

Working sample of app.js

var express = require("express");
var app = express();
var port = process.env.PORT || 3000;
var myData = require("./lib/my-data.js");

app.engine(".html", require("ejs").__express);
app.set("views", __dirname + "/views");
app.set("view engine", "html");
app.use(express.static(__dirname));

// Line below is what I'm trying to achieve.
//app.get("/get-data", myData.getData(request, response));

// Working line
app.get("/get-data", function(request, response) {
    myData.getData(request, response);
});

app.get("*", function (request, response) {
    response.render("index");
});

app.listen(port, function () {
    console.log("Listening on port " + port);
});

It bothers me that the line app.get("/get-data", myData.getData(request, response)); doesn't work while

app.get("/get-data", function(request, response) {
        myData.getData(request, response);
});

does.

What is the difference between the two approach?

I prefer using the first one since it's clean and precise but I can't seem to make it work.

Answer 1

app.get("/get-data", myData.getData); fixes this issue.

app.get allows you to supply a callback function , which is the one that you supply as the second parameter.

I'm going to simplify this problem and call that function get(string, func) . Inside this function, typically it's going to call the function that you supplied:

function get(string, func) {
  var request = "foo";
  var response = "bar";
  // ...
  func(request, response);
}

So you have to pass the name of the function for it to correctly call your function, therefore app.get("/get-data", myData.getData); works.

However, If you supply the second parameter as this get("/get-data", myData.getData(request, response)); , as in your first case, you are no longer supplying the func parameter with a function but just a value returned from your myData.getData(...) function.

For example, if your function is this:

function getData(req, res) {
  return 1;
}

The get function will end up doing something like:

get("foo", 1) {
  // ...
  1(request, response);
}

In the second case:

app.get("/get-data", function(request, response) {
  myData.getData(request, response);
});

This now passes an anonymous function as the callback and inside it you are just calling your own function and therefore will work as expected.