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

Exception or error:

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");

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!

How to solve:

Using res.json with Express:

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


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"


var objToJson = { };
objToJson.response = response;

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


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

var 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.


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.


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


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';

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