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Fix Metric types for better TypeScript support #356
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fixes #358 |
// Set defaults | ||
opts = opts || {}; | ||
|
||
let metric = initMetric('TTFB'); | ||
let report = bindReporter( | ||
onReport, | ||
onReport as ReportCallback, |
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I think this is probably fine for now since this is internal code...
...but if we're going to be exporting metric-specific versions of all of these types, it seems like ideally we would be able to make the bindReporter()
function understand those types as well. E.g. something similar to what we do here:
Lines 40 to 44 in 1d2c191
export const observe = <K extends keyof PerformanceEntryMap>( | |
type: K, | |
callback: (entries: PerformanceEntryMap[K]) => void, | |
opts?: PerformanceObserverInit | |
): PerformanceObserver | undefined => { |
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I couldn't figure out a way to do this as the metrics are not the same (particularly attribution has an extra attribution
attribute). But open to pointers here.
Also, unlike in the observe
example (where the specific type had to be passed on to the observer), we're treating all the metrics the same in bindreporter
, so seemed easier to just assert this as a ReportCallback type and not treat them as the 12 individual types (6 metrics, and 6 metrics with attribution).
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Gotcha. I think it may be possible, but I don't think it's worth spending time figuring out so 👍
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Yeah, it's the mismatch between the specific callbacks for the on*
methods (e.g. TTFBReportCallback
for onTTFB()
), and the fact that bindReporter()
currently requires its onReport
to be able to handle any of the metrics (which e.g. TTFBReportCallback
purposefully doesn't) that you get the type error and the need for the type assertion.
I'm happy to take a stab at parameterizing bindReporter
after this PR lands. Because bindReporter
truly doesn't care about the handler internally, it should be relatively disruption-free type rearranging (and I believe should streamline some metric type stuff at the same time).
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PR in #359
Fixes #351
Fixes #358
It appears you can't just change a type of an interface in Typescript by repeating it.
This PR uses
Omit
to completely replace themetric
value, but then has to do an assertion forReportCall
of the more specific metricXXXReportCall
type to the genericReportCall
type.