JavaScript/jQuery Charts - Load Data On Demand

In this demo, the range area Chart loads data as you pan it. Once the component loads a data block, this data stays in memory to reduce requests to the server.

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Backend API

$(() => { const HALFDAY = 43200000; let packetsLock = 0; $('#chart').dxChart({ dataSource: new DevExpress.data.DataSource({ store: [], sort: 'date', paginate: false, }), title: 'Temperature in Toronto (2017)', zoomAndPan: { argumentAxis: 'pan', }, scrollBar: { visible: true, }, argumentAxis: { argumentType: 'datetime', wholeRange: [new Date(2017, 0, 1), new Date(2017, 11, 31)], visualRange: { startValue: new Date(2017, 3, 1), length: { weeks: 2, }, }, visualRangeUpdateMode: 'keep', }, valueAxis: { name: 'temperature', allowDecimals: false, title: { text: 'Temperature, °C', font: { color: '#ff950c', }, }, label: { font: { color: '#ff950c', }, }, }, series: [{ color: '#ff950c', type: 'rangeArea', argumentField: 'date', rangeValue1Field: 'minTemp', rangeValue2Field: 'maxTemp', name: 'Temperature range', }], onOptionChanged(e) { if (e.fullName === 'argumentAxis.visualRange') { onVisualRangeChanged(e.value, e.component); } }, animation: { enabled: false, }, loadingIndicator: { backgroundColor: 'none', font: { size: 14, }, }, legend: { visible: false, }, }); function onVisualRangeChanged(visualRange, component) { const items = component.getDataSource().items(); if (!items.length || items[0].date - visualRange.startValue >= HALFDAY || visualRange.endValue - items[items.length - 1].date >= HALFDAY) { uploadDataByVisualRange(visualRange, component); } } function uploadDataByVisualRange(visualRange, component) { const dataSource = component.getDataSource(); const storage = dataSource.items(); const ajaxArgs = { startVisible: getDateString(visualRange.startValue), endVisible: getDateString(visualRange.endValue), startBound: getDateString(storage.length ? storage[0].date : null), endBound: getDateString(storage.length ? storage[storage.length - 1].date : null), }; if (ajaxArgs.startVisible !== ajaxArgs.startBound && ajaxArgs.endVisible !== ajaxArgs.endBound && !packetsLock) { packetsLock += 1; component.showLoadingIndicator(); getDataFrame(ajaxArgs) .then((dataFrame) => { packetsLock -= 1; const componentStorage = dataSource.store(); dataFrame.forEach((item) => { componentStorage.insert(item); }); dataSource.reload(); const range = component.getArgumentAxis().visualRange(); onVisualRangeChanged(range, component); }, () => { packetsLock -= 1; dataSource.reload(); }); } } function getDataFrame(args) { const deferred = $.Deferred(); $.ajax({ url: 'https://js.devexpress.com/Demos/WidgetsGallery/data/temperatureData', dataType: 'json', data: args, success(result) { deferred.resolve(result.map((i) => ({ date: new Date(i.Date), minTemp: i.MinTemp, maxTemp: i.MaxTemp, }))); }, error() { deferred.reject('Data Loading Error'); }, timeout: 2000, }); return deferred.promise(); } function getDateString(dateTime) { return dateTime ? dateTime.toLocaleDateString('en-US') : ''; } });

<!DOCTYPE html> <html xmlns="http://www.w3.org/1999/xhtml" lang="en"> <head> <title>DevExtreme Demo</title> <meta http-equiv="X-UA-Compatible" content="IE=edge" /> <meta http-equiv="Content-Type" content="text/html; charset=utf-8" /> <meta name="viewport" content="width=device-width, initial-scale=1.0, maximum-scale=5.0" /> <script src="https://ajax.googleapis.com/ajax/libs/jquery/3.5.1/jquery.min.js"></script> <script>window.jQuery || document.write(decodeURIComponent('%3Cscript src="js/jquery.min.js"%3E%3C/script%3E'))</script> <link rel="stylesheet" type="text/css" href="https://cdn3.devexpress.com/jslib/24.1.6/css/dx.light.css" /> <script src="js/dx.all.js"></script> <link rel="stylesheet" type="text/css" href="styles.css" /> <script src="index.js"></script> </head> <body class="dx-viewport"> <div class="demo-container"> <div id="chart"></div> </div> </body> </html>

#chart { height: 440px; }

To implement this functionality, do the following:

Configure a data source.
- Assign a DataSource with an empty store to the Chart dataSource property.
- Set the sort property to date.
- Disable the paginate property to prevent data from partitioning.
Configure the Chart to support on-demand data loading.
- Set the visualRangeUpdateMode property to keep.
- Specify a loadingIndicator.
- Specify the initial visualRange.
- Implement a function that respond to user pan operations and tracks visualRange changes. If a user changed the visual range, initiate a request for additional data.
Implement functions that load the data.
- In this demo, Chart displays daily information. If a user pan the Chart left or right more than half a day, additional data starts to load. The onVisualRangeChanged initiates this procedure.
- The uploadDataByVisualRange function analyzes the starting and ending points of the visual range and the bounds of already loaded data. If necessary, it calls the getDataFrame function to obtain new data points. Finally, it reloads the DataSource and saves the current visual range.
- The getDataFrame Ajax request gets the new data frame from the server.