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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, target (scope), arguments, fn (source function of the action yes
transaction name, target (scope) yes
scheduled-reaction object (Reaction instance) no
reaction object (Reaction instance), fn (source of the reaction) yes
compute object (ComputedValue instance), target (scope), fn (source) 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.

It is possible to emit your own spy events as well. See extras.spyReport, extras.spyReportStart and extras.spyReportEnd