Responding with a JSON object in Node.js (converting object/array to JSON string)

Question

I'm a newb to back-end code and I'm trying to create a function that will respond to me a JSON string. I currently have this from an example

function random(response) {
  console.log("Request handler 'random was called.");
  response.writeHead(200, {"Content-Type": "text/html"});

  response.write("random numbers that should come in the form of json");
  response.end();
}

This basically just prints the string "random numbers that should come in the form of JSON". What I want this to do is respond with a JSON string of whatever numbers. Do I need to put a different content-type? should this function pass that value to another one say on the client side?

Thanks for your help!

res.json({"Key": "Value"}); – Amol M Kulkarni Oct 08 '15 at 11:15 — Amol M Kulkarni, Oct 08 '15 at 11:15

Kevin Reilly · Accepted Answer · 2017-12-04T06:25:36.647

Using res.json with Express:

function random(response) {
  console.log("response.json sets the appropriate header and performs JSON.stringify");
  response.json({ 
    anObject: { item1: "item1val", item2: "item2val" }, 
    anArray: ["item1", "item2"], 
    another: "item"
  });
}

Alternatively:

function random(response) {
  console.log("Request handler random was called.");
  response.writeHead(200, {"Content-Type": "application/json"});
  var otherArray = ["item1", "item2"];
  var otherObject = { item1: "item1val", item2: "item2val" };
  var json = JSON.stringify({ 
    anObject: otherObject, 
    anArray: otherArray, 
    another: "item"
  });
  response.end(json);
}

score 79 · Answer 2 · edited Apr 27 '16 at 20:43

79

var objToJson = { };
objToJson.response = response;
response.write(JSON.stringify(objToJson));

If you alert(JSON.stringify(objToJson)) you will get {"response":"value"}

edited Apr 27 '16 at 20:43

falsarella

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answered May 05 '11 at 06:38

druveen

1,611
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Beware that res.write(JSON.stringify()) still wait for you to "end" the response. (res.end()) ; express .json() to this for you – 131 Jun 04 '15 at 09:55

score 25 · Answer 3 · edited May 23 '17 at 12:34

25

You have to use the JSON.stringify() function included with the V8 engine that node uses.

var objToJson = { ... };
response.write(JSON.stringify(objToJson));

Edit: As far as I know, IANA has officially registered a MIME type for JSON as application/json in RFC4627. It is also is listed in the Internet Media Type list here.

edited May 23 '17 at 12:34

Community

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answered May 05 '11 at 04:29

tyronegcarter

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Should the content-type header also be set to application/json or something like that? What is best practice for this? – ampersand May 05 '11 at 05:23
1

Yes, to make it a valid response the client will understand. Add: res.writeHead(200, {'Content-Type': 'application/json'}) before – Ali Dec 17 '12 at 13:50

score 13 · Answer 4 · edited May 23 '17 at 10:31

13

Per JamieL's answer to another post:

Since Express.js 3x the response object has a json() method which sets all the headers correctly for you.

Example:
res.json({"foo": "bar"});

edited May 23 '17 at 10:31

Community

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answered Jan 02 '15 at 23:42

Greg

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How can I do the same with a JSON file? – HGB Sep 26 '15 at 19:33
dont forget res.end() if you use this, I needed it – Charles Harring Apr 01 '19 at 07:07

score 3 · Answer 5 · edited Apr 20 '14 at 17:17

in express there may be application-scoped JSON formatters.

after looking at express\lib\response.js, I'm using this routine:

function writeJsonPToRes(app, req, res, obj) {
    var replacer = app.get('json replacer');
    var spaces = app.get('json spaces');
    res.set('Content-Type', 'application/json');
    var partOfResponse = JSON.stringify(obj, replacer, spaces)
        .replace(/\u2028/g, '\\u2028')
        .replace(/\u2029/g, '\\u2029');
    var callback = req.query[app.get('jsonp callback name')];
    if (callback) {
        if (Array.isArray(callback)) callback = callback[0];
        res.set('Content-Type', 'text/javascript');
        var cb = callback.replace(/[^\[\]\w$.]/g, '');
        partOfResponse = 'typeof ' + cb + ' === \'function\' && ' + cb + '(' + partOfResponse + ');\n';
    }
    res.write(partOfResponse);
}

Is this for sending back javascript functions? Am i getting this right? And why would you do that? Just curious — Sam Vloeberghs, Apr 20 '14 at 17:13

Soura Ghosh · Answer 6 · 2020-06-05T16:00:44.313

const http = require('http');
const url = require('url');

http.createServer((req,res)=>{

    const parseObj =  url.parse(req.url,true);
    const users = [{id:1,name:'soura'},{id:2,name:'soumya'}]

    if(parseObj.pathname == '/user-details' && req.method == "GET") {
        let Id = parseObj.query.id;
        let user_details = {};
        users.forEach((data,index)=>{
            if(data.id == Id){
                user_details = data;
            }
        })
        res.writeHead(200,{'x-auth-token':'Auth Token'})
        res.write(JSON.stringify(user_details)) // Json to String Convert
        res.end();
    }
}).listen(8000);

I have used the above code in my existing project.

score -2 · Answer 7 · answered Aug 08 '21 at 04:38

The JSON.stringify() method converts a JavaScript object or value to a JSON string, optionally replacing values if a replacer function is specified or optionally including only the specified properties if a replacer array is specified.

response.write(JSON.stringify({ x: 5, y: 6 }));

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Responding with a JSON object in Node.js (converting object/array to JSON string)

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