spy.md

sidebar_label	title	hide_title
spy [🚀]	Spy	true

Spy [🚀]

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 developer tools.

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.

type	observableKind	other fields	nested
action		name, object (scope), arguments[]	yes
scheduled-reaction		name	no
reaction		name	yes
compute		name	no
error		name, message, error	no
add	object	name, object, key, newValue	yes
update	object	name, object, key, newValue, oldValue	yes
remove	object	name, object, key, oldValue	yes
update	array	name, object (the array), index, newValue, oldValue	yes
splice	array	name, object (the array), index, added, removed, addedCount, removedCount	yes
add	map	name, object (observable map instance), key, newValue	yes
update	map	name, object (observable map instance), key, newValue, oldValue	yes
delete	map	name, object (observable map instance), key, oldValue	yes
add	set	name, object (observable set instance), newValue	yes
delete	set	name, object (observable set instance), oldValue	yes
create	box	object (Observable box instance), newValue	yes
update	box	object (Observable box instance), newValue, oldValue	yes
report-end		spyReportEnd=true, time? (total execution time in ms)	no

The report-end events 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.