Question

I am trying to simulate data to a function that would usually receive a JSON parsed data structure. When running this I get an error TypeError: can't convert undefined to object here: data.targets[i] = {

What am I doing wrong?

function SendFakeTargets(maxTargets, interval) {
    var data = {};
    data.timestamp = +new Date;

    var time = data.timestamp * 0.0005;
    var x = Math.sin(time) * 192 + 256;
    var y = Math.cos(time * 0.9) * 192 + 256;

    console.log(x, y);

    for (var i = 0; i < maxTargets; i++) {
        console.log(i);

        data.targets[i] = { //error is here
            id: i,
            x: x + (i * 10),
            y: y + (i * 10)
        };
    }

    HandleTargetData(data);

    setTimeout("SendFakeTargets("+maxTargets+", "+interval+")", interval);
}

Answer 1

you should previously declare

data.targets = [];

before using data.targets[i] inside the loop, otherwise data.targets is undefined. In a shorter way you could write

var data = {
    timestamp : +new Date,
    targets   : []
};

---

And as a side note, never use strings in setTimeout/Interval. Do instead

 setTimeout(function() {
      SendFakeTargets(maxTargets, interval);
 }, interval);