Tips for extracting information from Firebase and showing it on a Google gauge chart

Question

Tips for extracting information from Firebase and showing it on a Google gauge chart

I'm having some trouble displaying data from Firebase on a gauge chart. I keep getting an error that says "Uncaught (in promise)". Here's the JavaScript code I've been working with:

<script type="text/JavaScript">
  google.charts.load('current', {'packages':['gauge']});
  google.charts.setOnLoadCallback(drawChart);

  function drawChart() {
      var database = firebase.database();
         var Temperature;
            database.ref().on("value", function(snap){
                
                Temperature= snap.val().Temperature;
                
        });

    var data = google.visualization.arrayToDataTable([
      ['Label', 'Value'],
      ['Memory', Temperature]
    ]);

    var options = {
      width: 400, height: 120,
      redFrom: 90, redTo: 100,
      yellowFrom:75, yellowTo: 90,
      minorTicks: 5
    };

    var chart = new google.visualization.Gauge(document.getElementById('chart_div'));

    chart.draw(data, options);

    
  }
</script>

javascript firebase firebase-realtime-database

Answer 1

Answer №1

When pulling data from Firebase, it is important to remember that the process is asynchronous. This means that there might be a delay in fetching the data. While the data is being loaded, your main code will continue to run, leading to instances where certain functions get executed before the data is available.

In situations like this, such as when using chart.draw(data, options) before retrieving actual temperature data with

Temperature= snap.val().Temperature

, it can result in an empty chart since the necessary data hasn't been fetched yet.

To address this issue, it's crucial to ensure that any code relying on database data is placed inside the callback function or called from there directly. One possible solution involves restructuring your code as follows:

function drawChart() {
    var database = firebase.database();
    var Temperature;

    var options = {
        width: 400, height: 120,
        redFrom: 90, redTo: 100,
        yellowFrom:75, yellowTo: 90,
        minorTicks: 5
    };

    var chart = new google.visualization.Gauge(document.getElementById('chart_div'));

    database.ref().on("value", function(snap){
        Temperature= snap.val().Temperature;
                
        var data = google.visualization.arrayToDataTable([
            ['Label', 'Value'],
            ['Memory', Temperature]
        ]);
        chart.draw(data, options);
    });
}

For further insights, you may refer to:

Understanding Why Firebase Loses Reference Outside the once() Function

Answer 2

When pulling data from Firebase, it is important to remember that the process is asynchronous. This means that there might be a delay in fetching the data. While the data is being loaded, your main code will continue to run, leading to instances where certain functions get executed before the data is available.

In situations like this, such as when using chart.draw(data, options) before retrieving actual temperature data with

Temperature= snap.val().Temperature

, it can result in an empty chart since the necessary data hasn't been fetched yet.

To address this issue, it's crucial to ensure that any code relying on database data is placed inside the callback function or called from there directly. One possible solution involves restructuring your code as follows:

function drawChart() {
    var database = firebase.database();
    var Temperature;

    var options = {
        width: 400, height: 120,
        redFrom: 90, redTo: 100,
        yellowFrom:75, yellowTo: 90,
        minorTicks: 5
    };

    var chart = new google.visualization.Gauge(document.getElementById('chart_div'));

    database.ref().on("value", function(snap){
        Temperature= snap.val().Temperature;
                
        var data = google.visualization.arrayToDataTable([
            ['Label', 'Value'],
            ['Memory', Temperature]
        ]);
        chart.draw(data, options);
    });
}

For further insights, you may refer to:

Understanding Why Firebase Loses Reference Outside the once() Function

Tips for extracting information from Firebase and showing it on a Google gauge chart

Answer №1

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