如何发送从文件读取的数据作为 NodeJS 中快速路由的响应？

Question

I have a JSON file in local folder with a structure like this.

{
   license: "abcd",
   name: "abcd",

   data: [
      Array of JSON Objects ....
   ]
}

I want to access the data array in the Object and send it as response from express route This is what I tried.

import express from "express";
import fs from "fs";
import bodyParser from "body-parser";

var app = express();
app.use(bodyParser.json());

var fileData: string = fs.readFileSync("path to json file", { encoding: 'utf-8' });
var jsonData = JSON.parse(fileData).data;

console.log(jsonData);

app.get("/getJsonData", (err, res) => {
    if (err)
        throw err;

    res.send(JSON.stringify(jsonData));
});

app.listen("3001", () => console.log("listening at 3001"));

It shows correct json when I log it outside the express route function, but inside the function the response is [object Object] with status code of 500 (Internal Server Error).

I tried the asynchronous method also

var app = express();
app.use(bodyParser.json());

app.get("/getJsonData", (err, res) => {
    if (err)
        throw err;

    fs.readFile("path to json file", (fileErr, result) => {
        if(fileErr) throw fileErr;

        var jsonData = JSON.parse(result.toString()).data;

        res.json(jsonData);
    });
    
});

but I get the same response as [object Object] and status code 500. I tried res.send(JSON.stringify(jsonData)) but no use. How can I send the json data that I get from file to frontend using Express?? btw I am using TypeScript for this.

Answer 1

This line

app.get("/getJsonData", (err, res) => 

The err is not an error, its the request it should be:

app.get("/getJsonData", (req, res) => {
    res.send(JSON.stringify(jsonData));
});

Its literally at the example Hello world site of express.js, there you will sees that they use req

https://expressjs.com/de/starter/hello-world.html

The reason why you always get an 500 error is because err , wich is obviously the request, is always truthy

You also dont need to Stringify it, you could just do res.json(jsonData)

Answer 2

If you want to send a json object between your express server and the client, you'll need to send the data via res.json(obj) where obj must explicitly be a JSON object (can't be an array of JSON objects). What you can do to just send the array, is simply wrap your jsonData array inside a bracket pair and you are done.

let jsonData = JSON.parse(fileData).data;
res.json({ jsonData });
//or if you dont understand the above use
res.json({ jsonData: jsonData})
//which is equivalent to the above line