JavaScript callback function seems to work, but does not draw the data

Question

I've already been through many tutorials on callbacks (eg here , on SO and this gem )
By far the best one was this gem . Especially this part helped me to understand.

function addOne(thenRunThisFunction) {
  waitAMinuteAsync(function waitedAMinute() {
    thenRunThisFunction()
  })
}

addOne(function thisGetsRunAfterAddOneFinishes() {})

So I implemented it as described there. Now everything seems to work on console output, but it does not render my d3 force directed graph as expected.

[some fancy variables used by force graph]

function draw(json) {
    java.alert(json);
    [awsome force graph stuff]
};

var data = undefined;

function readInputStream(callback){
    data = java.getJSONObject();
    if(!data == ""){
        java.alert("success");
    } else {
        java.alert("failure");
    }
    callback();
}

function prepareDraw() {
    java.alert("prepare called");
    draw(data);
}

readInputStream(prepareDraw);

Please note that java is an identifier. I'm running it all in a JavaFX WebView and all methods after java. are actual java methods I use in JavaScript. See this:

public class JStoFXBridge {
    private String json;

    public String getJSONObject(){
        return json;
    }
    public void setJSONObject(String string){
        this.json = string;
    }
    public void alert(String alert){
        System.out.println("Alert: " + alert);
    }
}

Now my console prints:

Alert: success
Alert: prepare called
Alert: {"nodes":[{"name":"sepp","id":0,"group":2},{"name":"hans","id":1,"group":6}, [...]

Which is the right format for my JSON String and which is (as far as I see it) in the right order to be executet. data gets filled and is not empty. the callback method gets called. My draw function has a filled & valid JSON String. What is going wrong here? I have no explination why this won't work.

Answer 1

Sometimes it's easier than you think...

java.alert("prepare called");
var json = JSON.parse(data);
draw(json);

Problem: data was a String, d3 wants a JSON Object. Watch here . New output:

Alert: success
Alert: prepare called
Alert: [object Object]

Now renders the graph just fine. var data = {"nodes":[{"name":"sepp", [...] works because JavaScript interpretes it as a JSON Object.