Custom inspection warning

[ivan-kleshnin]

Version: 10.3.0
Platform: OS-x
Subsystem: –

Something is broken about deprecation warning on .inspect. Honestly, I never heard of this method (Node's magic stuff?) But at this moment all libraries having objects with inspect method in their APIs are affected.

> {inspect: () => null}
null
> (node:1278) [DEP0079] DeprecationWarning: Custom inspection function on Objects via .inspect() is deprecated

One example of such library: https://github.com/origamitower/folktale

[jdalton]

Hi @ivan-kleshnin!

This is because in Node 6.6.0 a symbol util.inspect.custom was added and the old behavior of using a method named inspect was deprecated. For more info on custom inspection see this. Eventually, the documentation deprecation became a runtime deprecation. You're seeing this in the REPL because under the hood the REPL uses util.inspect().

The deprecation and legacy functionality will be removed in Node 11 (#20722)

It does seem odd that the REPL use should trigger the deprecation warning since it's a side-effect of the REPL implementation. The simplest way to handle this in core would be with process.noDeprecation=true before the util.inspect() call and reset after.

For user-land a temporary workaround could be to add a non-function value of the util.inspect.custom symbol

Reflect.defineProperty(folktale, util.inspect.custom, {
  value: ""
})

[ivan-kleshnin]

Ok, got it. Thank your for the explanation! Closing...