How to return JSON in Express

Question

I'm new to node/express. I have a simple express app with one post route ('/'). Given a list of GitHub users names, it should return information about those developers.

For example, if I post

{ "developers": ["JohnSmith", "JaneDoe"] }

It should return

[
  {
    "bio": "Software Engineer at Google",
    "name": "John Smith"
  },
  {
    "bio": "Product Manager, Microsoft",
    "name": "Jane Doe"
  }
]

This is what I have so far

const express = require('express');
const axios = require('axios');
const app = express();
app.use(express.json());

app.post('/', function(req, res, next) {
  try {
    let results = req.body.developers.map(async d => {
      return await axios.get(`https://api.github.com/users/${d}`);
    });
    let out = results.map(r => ({ name: r.data.name, bio: r.data.bio }));    
    return res.send(out);
  } catch {
    next(err);
  }
});

app.use((err, req, res, next) => {
  res.send("There was an error");
})

app.listen(3000, function(){
  console.log("Server started on port 3000!");
});

When I try this in a tool like Insomnia, I keep getting There was an error.

Does this answer your question? [Use async await with Array.map](https://stackoverflow.com/questions/40140149/use-async-await-with-array-map) — evolutionxbox, May 11 '21 at 15:52
@EA6923 check this https://stackoverflow.com/questions/19696240/proper-way-to-return-json-using-node-or-express — user123456, May 11 '21 at 15:53
I think it is easy as res.send( JSON.stringify("There was an error")); — user123456, May 11 '21 at 15:54
@user123456 that will result in `"\"There was an error\""` which is probably not what is desired. — evolutionxbox, May 11 '21 at 15:55
@evolutionxbox he will always return res.send("There was an error");, he should terminate the response, he asked how do I return json, I think what he wants to know what is missing in his logic to return the formatted json he already gve — user123456, May 11 '21 at 19:21

score 1 · Answer 1 · answered May 11 '21 at 18:33

1

The way you return JSON in an Express API is as follows:

res.status(200).json(out)

See https://expressjs.com/it/api.html for the full documentation.

answered May 11 '21 at 18:33

Mattia Rasulo

1,236
10
15

score 0 · Answer 2 · answered May 11 '21 at 18:18

0

You can use res.formate() as per this docs...

Or set type for res as per this Docs...

res.type('json')

answered May 11 '21 at 18:18

JeX

95
1
10

score 0 · Answer 3 · answered May 11 '21 at 18:26

From middleware, you are always saying res.json("there is some error"), why are you keeping it there if not needed. if you remove app.use(). you will see the request is returning you names of the developer

read this for error handling. https://expressjs.com/en/guide/error-handling.html

score 0 · Answer 4 · answered May 13 '21 at 06:59

You're getting There was an error. Because, there is an error in your / route. But, the thing is you haven't wrote the err parameter with catch. If add that one in your catch (of your try/catch block) and console.log it, you'll see the error

TypeError: Cannot read property 'name' of undefined

You're getting this error because, results variable is actually an array of pending Promise. You need to first resolve these pending promises. One way to do is,

app.post("/", function (req, res, next) {
  try {
    const developers = req.body.developers;
    let promises = [];
    developers.map((d) => {
      promises.push(axios.get(`https://api.github.com/users/${d}`));
    });

    Promise.all(promises).then((responses) => {
      let out = responses.map((r) => ({
        name: r.data.name,
        bio: r.data.bio,
      }));

      return res.send(out);
    });
  } catch (err) {
    next(err);
  }
});

How to return JSON in Express

4 Answers4