Question

I’m trying to read in JSON objects over a websocket for visualisation by the D3 library. I’m just checking if the browser receives the JSON correctly. This is the code:

 ws = new WebSocket("ws://localhost:8888/dh");

      ws.onmessage = function(evt)
      {
        d3.json(
        JSON.parse(evt.data),
        function (jsondata) {

        console.log(jsondata);

        var data = jsondata.map(function(d) { return d.Value; });
        console.log(data);

            });   
      }

But when I check the console log it gives me these errors:

[19:15:36.434] TypeError: jsondata is null @ http://localhost:8888/static/anEx.js:21

and console.log(data) is null.

What is incorrect here?

Thanks

Answer 1

d3.json is used to make HTTP requests that return JSON responses.

You already have the data in your WS message handler, there’s no need to make another request. Just do:

ws.onmessage = function(evt) {
    var jsondata = JSON.parse(evt.data);
    console.log(jsondata);
    // handle data ...
}