On 1/11/17 6:43 AM, Isiah Meadows wrote:
Not if it's (likely) throwing from the `new Error`.
It's not. The "stack" property in V8 quacks like a value property for the most part, but the first access to it invokes some code that does the (lazy) stack string construction. That process involves calling Error.prepareStackTrace if such a thing exists.
Specifically, as of today, see https://github.com/v8/v8/blob/d5a0860e87b5f8d88432cf628f4bbc0cc922317f/src/messages.cc#L927-L954 which is called from https://github.com/v8/v8/blob/d5a0860e87b5f8d88432cf628f4bbc0cc922317f/src/accessors.cc#L1169
The whole setup is basically designed to have things that look like data properties but actually involve executing code to compute the property value (and possibly executing code when the "value" property is set).
SpiderMonkey has similar things as well, though we've been getting rid of them as much as possible. The obvious one that remains is .length on Array objects. This allows Array objects to be non-exotic for practical purposes in terms of their engine representation, and hence not suffer the performance penalties exotic objects suffer. In spec terms, of course, Array instances are just exotic objects. In an ideal world, the implementation detail is just that and is not observable....
-Boris _______________________________________________ es-discuss mailing list [email protected] https://mail.mozilla.org/listinfo/es-discuss
