Load Data On Demand

import React from 'react'; import DataSource from 'devextreme/data/data_source'; import { Chart, ZoomAndPan, ScrollBar, ArgumentAxis, ValueAxis, Title, Label, Font, Legend, Series, Animation, LoadingIndicator } from 'devextreme-react/chart'; const wholeRange = { startValue: new Date(2017, 0, 1), endValue: new Date(2017, 11, 31) }; class App extends React.Component { constructor(props) { super(props); this.packetsLock = 0; this.HALFDAY = 43200000; this.chartDataSource = new DataSource({ store: [], sort: 'date', paginate: false }); this.state = { visualRange: { startValue: new Date(2017, 3, 1), endValue: new Date(2017, 3, 15) } }; this.handleChange = this.handleChange.bind(this); } render() { return ( <Chart id="chart" title="Temperature in Toronto (2017)" dataSource={this.chartDataSource} onOptionChanged={this.handleChange} > <ZoomAndPan argumentAxis="pan" /> <ScrollBar visible={true} /> <ArgumentAxis argumentType="datetime" visualRangeUpdateMode="keep" visualRange={this.state.visualRange} wholeRange={wholeRange} /> <ValueAxis name="temperature" allowDecimals={false} > <Title text={'Temperature, &deg;C'}> <Font color="#ff950c" /> </Title> <Label> <Font color="#ff950c" /> </Label> </ValueAxis> <Series color="#ff950c" type="rangeArea" argumentField="date" rangeValue1Field="minTemp" rangeValue2Field="maxTemp" name="Temperature range" /> <Animation enabled={false} /> <LoadingIndicator backgroundColor="none"> <Font size={14} /> </LoadingIndicator> <Legend visible={false} /> </Chart> ); } handleChange(e) { if(e.fullName === 'argumentAxis.visualRange') { const stateStart = this.state.visualRange.startValue; const currentStart = e.value.startValue; if(stateStart.valueOf() !== currentStart.valueOf()) { this.setState({ visualRange: e.value }); } this.onVisualRangeChanged(e.component); } } onVisualRangeChanged(component) { const items = component.getDataSource().items(); const visualRange = this.state.visualRange; if(!items.length || items[0].date - visualRange.startValue >= this.HALFDAY || visualRange.endValue - items[items.length - 1].date >= this.HALFDAY) { this.uploadDataByVisualRange(visualRange, component); } } 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 && !this.packetsLock) { this.packetsLock++; component.showLoadingIndicator(); getDataFrame(ajaxArgs) .then(dataFrame => { this.packetsLock--; dataFrame = dataFrame.map(i => { return { date: new Date(i.Date), minTemp: i.MinTemp, maxTemp: i.MaxTemp }; }); const componentStorage = dataSource.store(); dataFrame.forEach(item => componentStorage.insert(item)); dataSource.reload(); this.onVisualRangeChanged(component); }) .catch(() => { this.packetsLock--; dataSource.reload(); }); } } } function getDataFrame(args) { let params = '?'; params += `startVisible=${args.startVisible} &endVisible=${args.endVisible} &startBound=${args.startBound} &endBound=${args.endBound}`; return fetch(`https://js.devexpress.com/Demos/WidgetsGallery/data/temperatureData${params}`) .then(response => response.json()); } function getDateString(dateTime) { return dateTime ? dateTime.toLocaleDateString('en-US') : ''; } export default App;