spy.md

sidebar_label	title	hide_title
spy	Spy	true

Spy

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Usage: spy(listener). Registers a global spy listener that listens to all events that happen in MobX. It is similar to attaching an observe listener to all observables at once, but also notifies about running (trans/re)actions and computations. Used for example by the mobx-react-devtools.

Example usage of spying all actions:

spy((event) => {
    if (event.type === "action") {
        console.log(`${event.name} with args: ${event.arguments}`)
    }
})

Spy listeners always receive one object, which usually has at least a type field. The following events are emitted by default by spy.

event	fields	nested
action	name, object (scope), arguments	yes
scheduled-reaction	name	no
reaction	name	yes
compute	name	no
error	message	no
update (array)	object (the array), index, newValue, oldValue	yes
update (map)	object (observable map instance), name, newValue, oldValue	yes
update (object)	object (instance), name, newValue, oldValue	yes
splice (array)	object (the array), index, added, removed, addedCount, removedCount	yes
add (map)	object, name, newValue	yes
add (object)	object, name, newValue	yes
delete (map)	object, name, oldValue	yes
create (boxed observable)	object (ObservableValue instance), newValue	yes

Note that there are events with the signature { spyReportEnd: true, time? }. These events might not have a type field, but they are part of an earlier fired event that had spyReportStart: true. This event indicates the end of an event and this way groups of events with sub-events are created. This event might report the total execution time as well.

The spy events for observable values are identical to the events passed to observe. See intercept & observe for an extensive overview.

In production builds, the spy API is a no-op as it will be minimized away.