Exception type for "invalid operations"?

Domenic Denicola domenic at domenicdenicola.com
Thu Jan 30 08:49:52 PST 2014


From: Allen Wirfs-Brock <allen at wirfs-brock.com>

> If you invert things you can think of "invalid operation" as trying to apply a valid operation upon the "wrong kind of object" so TypeError is a plausible.

This seems like a stretch :P. Are there existing instances in the ES spec of this kind of use? I guess maybe trying to write to a non-writable property in strict mode and the like.

> In practice, where would throwing OperationError instead of TypeError actually make any difference.  How would you handle one differently from the other?

In practice it makes almost no difference, just like all other ECMAScript error type discrimination. It just seems that when a user sees `TypeError` in a stack trace, they expect to find some kind of argument validation problem.

(Maybe once we get pattern-matching `catch` clauses it would matter more. E.g. people could purposefully try to catch `OperationError`s from such operations, and handle them differently, leaving `TypeError`s etc. to bubble outward and hit a top-level exception handler as "truly unexpected." But that's a ways off.)

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Sounds like `TypeError` is probably the way to go, even if it feels a bit off.


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