The JSON array retrieved from the $http.GET request is coming back as undefined, which is not expected

Question

The JSON array retrieved from the $http.GET request is coming back as undefined, which is not expected

Presenting my code below:

function gatherDataForGraph(unit, startTs, endTs, startState, endState){
points = [];
console.log('/file/tsDataPoints/'+unit+"?startDate="+startTs+"&endDate="+endTs+"&startState="+startState+"&endState="+endState);
$http.get('/file/tsDataPoints/'+unit+"?startDate="+startTs+"&endDate="+endTs+"&startState="+startState+"&endState="+endState).success(function(data){
    for (var i = 0; i < data.length; i++) {
        points.push({x:getBasicTimeFromEpoch(data[i].ts), y:data[i].data});
    }
  return points;
  });
}

function displayFileStateLineGraph(unit, startTs, endTs){
gatherDataForGraph(unit, startTs, endTs, 1, 2);

console.log(gatherDataForGraph(unit, startTs, endTs, 1, 2));
var dp1= gatherDataForGraph(unit, startTs, endTs, 1, 2);
var dp2= gatherDataForGraph(unit, startTs, endTs, 2,3);
var dp3 = gatherDataForGraph(unit, startTs, endTs, 3,4);
console.log(dp1);
console.log(dp2);
console.log(dp3);
var chart = new CanvasJS.Chart("chartContainer", {
    title: {
      text: "Click on legend items to hide/unhide dataseries"
    },
    legend: {
        cursor: "pointer",
        itemclick: function (e) {
            if (typeof (e.dataSeries.visible) === "undefined" || e.dataSeries.visible) {
                e.dataSeries.visible = false;
            } else {
                e.dataSeries.visible = true;
            }
            chart.render();
        }
    },
    data: [{
        showInLegend: true,
        type: "line",
        dataPoints: dp1
    }, {
        showInLegend: true,
        type: "line",
        dataPoints: dp2
    }, {
        showInLegend: true,
        type: "line",
        dataPoints: dp3
         }]
  });
  chart.render();
}
displayFileStateLineGraph("day",1404000000, 1406000000)

Upon running the console.logs, only "undefined" is shown. It's possible that this occurs because the function executes before the JSON call is complete. This issue seems unfamiliar to me.

javascript ajax json angularjs http-get

Answer 1

Answer №1

First and foremost, it's crucial to address the issue with your getLineGraphData function lacking a return value. Additionally, as this function runs asynchronously, you must ensure that you wait for the completion of the success handler before attempting to access the points data.

To rectify this, begin by incorporating a return statement in your code: return $http.get(...). This will result in the function returning a Promise.

Furthermore, in order to successfully access the points data, you need to utilize

promise.then(function(points) { ... })

. This grants you access to the retrieved data within the then function.

In scenarios where you depend on multiple sets of points, it is imperative to await the completion of all operations. You can achieve this by employing `$q.all(...)` method as illustrated below:

$q.all({
    dp1: getLineGraphData(unit, startTs, endTs, 1,2),
    dp2: getLineGraphData(unit, startTs, endTs, 2,3),
    dp3: getLineGraphData(unit, startTs, endTs, 3,4)
}).then(function(dataPoints) {
    var dp1 = dataPoints.dp1, dp2 = dataPoints.dp2, dp3 = dataPoints.dp3;
    ... Create your chart ...
});

Answer 2

First and foremost, it's crucial to address the issue with your getLineGraphData function lacking a return value. Additionally, as this function runs asynchronously, you must ensure that you wait for the completion of the success handler before attempting to access the points data.

To rectify this, begin by incorporating a return statement in your code: return $http.get(...). This will result in the function returning a Promise.

Furthermore, in order to successfully access the points data, you need to utilize

promise.then(function(points) { ... })

. This grants you access to the retrieved data within the then function.

In scenarios where you depend on multiple sets of points, it is imperative to await the completion of all operations. You can achieve this by employing `$q.all(...)` method as illustrated below:

$q.all({
    dp1: getLineGraphData(unit, startTs, endTs, 1,2),
    dp2: getLineGraphData(unit, startTs, endTs, 2,3),
    dp3: getLineGraphData(unit, startTs, endTs, 3,4)
}).then(function(dataPoints) {
    var dp1 = dataPoints.dp1, dp2 = dataPoints.dp2, dp3 = dataPoints.dp3;
    ... Create your chart ...
});

Answer 3

Answer №2

When working with the getLineGraphData function, ensure that you are handling the promise returned by $http.get properly. The points should be populated within the success callback of the promise, not directly from the getLineGraphData function itself. Make sure to return the promise from the function and then attach a success callback to it to populate dp1 and other variables accordingly.

 function getLineGraphData(unit, startTs, endTs, startState, endState){
    var points = [];
    console.log('/file/tsDataPoints/'+unit+"?startDate="+startTs+"&endDate="+endTs+"&startState="+startState+"&endState="+endState);
    return $http.get('/file/tsDataPoints/'+unit+"?startDate="+startTs+"&endDate="+endTs+"&startState="+startState+"&endState="+endState);
 }

var dp1 = [];
getLineGraphData(unit, startTs, endTs, 1, 2).success(function(data){
    for (var i = 0; i < data.length; i++) {
        dp1.push({x:getBasicTimeFromEpoch(data[i].ts), y:data[i].data});
    }
    console.log(dp1);
  });

Ensure that dp1 is successfully printed out as expected.

Answer 4

When working with the getLineGraphData function, ensure that you are handling the promise returned by $http.get properly. The points should be populated within the success callback of the promise, not directly from the getLineGraphData function itself. Make sure to return the promise from the function and then attach a success callback to it to populate dp1 and other variables accordingly.

 function getLineGraphData(unit, startTs, endTs, startState, endState){
    var points = [];
    console.log('/file/tsDataPoints/'+unit+"?startDate="+startTs+"&endDate="+endTs+"&startState="+startState+"&endState="+endState);
    return $http.get('/file/tsDataPoints/'+unit+"?startDate="+startTs+"&endDate="+endTs+"&startState="+startState+"&endState="+endState);
 }

var dp1 = [];
getLineGraphData(unit, startTs, endTs, 1, 2).success(function(data){
    for (var i = 0; i < data.length; i++) {
        dp1.push({x:getBasicTimeFromEpoch(data[i].ts), y:data[i].data});
    }
    console.log(dp1);
  });

Ensure that dp1 is successfully printed out as expected.

The JSON array retrieved from the $http.GET request is coming back as undefined, which is not expected

Answer №1

Answer №2

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