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Drop touch gestures that gain a finger the chart never saw - #238
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dygraphs records the touches of touchstart and, on a two-finger touchmove, reads initialTouches[1]. When the second finger lands outside the chart its touchstart never reaches the canvas, yet later touchmove events list both fingers, so moveTouch read initialTouches[1].pageX of undefined. touchMove now clears the stale gesture and ignores the event when it carries more touches than the gesture started with.
kapantzak
previously approved these changes
Sep 29, 2026
kapantzak
approved these changes
Sep 29, 2026
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Problem
Sentry NETDATA-INC-DNA (45 events in 24h, all on cloud-frontend 7.129.0 with charts 6.12.15):
Cannot read properties of undefined (reading 'pageX')in dygraphsmoveTouch(dygraph-interaction-model.js:525,initialTouches[1].pageX).The #237 guard (
generic.js) only checks thatcontext.initialTouchesexists. When the second finger lands outside the chart, itstouchstartnever reaches the canvas, so dygraphs records one touch, while latertouchmoveevents list both fingers. The production stack confirms the guard shipped: the throwing call is the line right afterif (!context.initialTouches) return.Change
touchMoveclears the stale gesture and ignores the event when it carries more touches than the gesture started with. Valid pans and two-finger pinches still delegate to dygraphs.Tests
touchstartthen a two-fingertouchmovewith no secondtouchstart. Before the fix it throws the productionTypeErroratdygraph-interaction-model.js:525:44viageneric.js:124.Release
cloud-frontend needs a charts release with this change and an
@netdata/chartsbump before DNA stops. Browser check still pending: pan, pinch, adding a finger outside the chart, double tap, on iOS Safari and Android Chrome.