JSON parse on a JSON string throws “Cannot convert object to primitive value”

Question

server.js

uses the body parser middleware, handlebars and express

route

module.exports = function (app) {
    app.post('/questionnaire/submit', function (req, res) { // Ajax Call
        var data = JSON.parse(req.body);
        res.send({});
    });
};

client

function submitData() { // Send a data object to the server
    $.ajax({
        type: 'POST',
        url: '/questionnaire/submit',
        dataType: "json",
        data: JSON.stringify({
            satisfactory: "text 1",
            improvement: "text 2",
            rating: 0.7
        })
    }).done(function () {
        $(location).attr('href', '/sendOff');
    }).fail(function () {

    });
}

when logging req.body I get a JSON string

{ '{"satisfactory":"text 1","improvement":"text 2","rating":0.7}': '' }

and I try to parse this string to an object. When I do so, I get this error message

  TypeError: Cannot convert object to primitive value at JSON.parse (<anonymous>) at C:\\Users\\mah\\Desktop\\FeedbackTool\\Server\\Routes\\questionnaire.js:12:25 at Layer.handle [as handle_request] (C:\\Users\\mah\\node_modules\\express\\lib\\router\\layer.js:95:5) at next (C:\\Users\\mah\\node_modules\\express\\lib\\router\\route.js:137:13) at Route.dispatch (C:\\Users\\mah\\node_modules\\express\\lib\\router\\route.js:112:3) at Layer.handle [as handle_request] (C:\\Users\\mah\\node_modules\\express\\lib\\router\\layer.js:95:5) at C:\\Users\\mah\\node_modules\\express\\lib\\router\\index.js:281:22 at Function.process_params (C:\\Users\\mah\\node_modules\\express\\lib\\router\\index.js:335:12) at next (C:\\Users\\mah\\node_modules\\express\\lib\\router\\index.js:275:10) at C:\\Users\\mah\\node_modules\\body-parser\\lib\\read.js:130:5 

so how can I parse the string to an object?

Normally I would execute JSON.parse(req.body) .

Answer 1

Since you are using body-parser middleware then you dont have to parse req.body again cause it already parsed by body-parser

Example

if you used app.use(bodyParser.json())

then you just have to do this

module.exports = function (app) {
    app.post('/questionnaire/submit', function (req, res) { // Ajax Call
        var data = req.body; // this is already parsed and is an object
        res.send({});
    });
};

as pointed out by @TJ Crowder you should also send the correct contentType so body-parser knows its json

function submitData() { // Send a data object to the server
    $.ajax({
        type: 'POST',
        url: '/questionnaire/submit',
        contentType: 'application/json',
        data: JSON.stringify({
            satisfactory: "text 1",
            improvement: "text 2",
            rating: 0.7
        })
    }).done(function () {
        $(location).attr('href', '/sendOff');
    }).fail(function () {

    });
}

Answer 2

dataType doesn't say what type of data you're sending , it says what type of response you expect. You need to say that you're sending JSON, via contentType: "application/json" in your ajax call. Details in the documentation . (You're not the first or only person, by far, to be tripped up by the naming of dataType .)

That's half the problem. See Stamos' answer for the other half.

Answer 3

You need to setup correct contentType:

$.ajax({
    type: 'POST',
    url: '/questionnaire/submit',
    contentType: 'application/json',
    data: JSON.stringify({ satisfactory: "text 1", rating: 0.7 })
});


app.post('/questionnaire/submit', function (req, res) { // Ajax Call
    var data = JSON.parse(req.body);
    console.log(data.rating); // 0.7
    res.send(data);
});

Also, with body-parser you may avoid JSON.parse calls on the server side, the link .