@can.getWhatIChange()

The @can.getWhatIChange symbol is added to make sure can-debug can report all the observables whose values are set by value-like observables.

This function iterates over the event handlers attached to the observable's value event and collects the result of calling @can.getChangesDependencyRecord on each handler; this symbol allows the caller to tell what observables are being mutated by the event handler when it is executed.

In the following example a can-simple-observable instance named month is created and when its value changes the age property of the map can-simple-map instance is set. The event handler that causes the mutation is then decatorated with @can.getChangesDependencyRecord to register the mutation dependency.

var month = new SimpleObservable(11);
var map = new SimpleMap({ age: 30 });
var canReflect = require("can-reflect");

var onValueChange = function onValueChange() {
map.set("age", 31);
};

onValueChange[canSymbol.for("can.getChangesDependencyRecord")] = function() {
return {
    keyDependencies: new Map([ [map, new Set(["age"])] ])
}
};

canReflect.onValue(month, onValueChange);
month[canSymbol.for("can.getWhatIChange")]();

The dependency records collected from the event handlers are divided into two categories:

• mutate: Handlers in the mutate/domUI queues
• derive: Handlers in the notify queue

Since event handlers are added by default to the "mutate" queue, calling @can.getWhatIChange on the month instance returns an object with a mutate property and the keyDependencies Map registered on the onValueChange handler.

If multiple event handlers were attached to month, the dependency records of each handler are merged by @can.getWhatIChange. Please check out the can-reflect-dependencies docs to learn more about how this symbol is used to keep track of custom observable dependencies.