javaScript property
JavaScript-based function code to be called.
If a dart-based function is also defined, this will be called in parallel.
The code runs inside function(...args){...}, so it can use this,
args, and event as a shorthand for args[0]:
HighchartsCallback(null, 'event.preventDefault();')
Call event.preventDefault() here rather than from a dart-based
callback. A dart-based callback receives only a JSON snapshot of the
event, delivered after the JavaScript function has already returned.
Implementation
final String? javaScript;