@@can.getValueDependencies()

The @@can.getValueDependencies symbol points to a function that returns an object containing all values that affect the value of this Value-like object. If the dependencies include properties on a Map-like object, they are placed in a [can-util/js/cid-map/cid-map CIDMap] keyed on keyDependencies in the return object. If the dependencies include the values of Value-like objects, they are placed in a [can-util/js/cid-set/cid-set CIDSet] keyed on valueDependencies. Return undefined if the value is not computed, or an empty object if a key is computed without external dependencies.

var someOtherObj;
// This is a clear but not very useful implementation of a computed value.
// We recommend can-observation for new development of computed values.
var val = function() { 
    return canReflect.getKeyValue(someOtherObj, "bar");
};
val.reads: [{ object: someOtherObj, key: "bar" }]

val[canSymbol.for("can.getValueDependencies")] = function(key) {
  var ret;
  if(this.reads) {
    ret = {};
    this.reads.forEach(function(read) {
        if(read.key) {
            ret.keyDependencies = ret.keyDependencies || new CIDMap();
            if(!ret.keyDependencies.has(read.object)) {
                ret.keyDependencies.add(read.object, []);
            }
            ret.keyDependencies.get(read.object).push(read.key);
        } else {
            ret.valueDependencies = ret.valueDependencies || new CIDMap();
            ret.valueDependencies.add(read.object);
        }
    });
  }
  return ret;
};