refactor(events): Introduce and use event type predicates #8538
+231
−74
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The basics
The details
Proposed Changes
Introduce predicates for testing
Abstract
event subclasses based on their.type
properties. These are useful because there are places where it is not possible to useinstanceof <ClassConstructor>
tests for type narrowing due to load ordering issues that would be caused by the need toimport
(rather than justimport type
) the classconstructors in question.
Simplify several sections of code by using these type predicates for type narrowing, and thereby avoiding the need for explicit casts.
Reason for Changes
Cleanup and preparation for fixing #8225 et al.
Test Coverage
npm test
.Additional Information
The type predicates are not currently reexported from
core/blockly.ts
. This could be done by adding suitableexport … from …
statements tocore/events/events.ts
, but I've opted not to do this until there is a good reason to: in most cases it is probably preferable that code usee instanceof EventClass
rather thanisEventClass(e)
, since the former is a stricter and less easily subverted type check, and code outside ofcore/
can always access the event constructors without any cyclicimport
issues.