@@can.keyHasDependencies(key)

The @@can.keyHasDependencies symbol points to a function that returns true if there are any other events or property changes that will change the value of the property on the context object with key key; false otherwise.
By convention, if an object implementation distinguishes between unbound objects or values, and those which are bound without external dependencies (as is the case with can-map), @@can.keyHasDependencies may return undefined for unbound objects instead of false.

var someOtherObj;
var obj = {
    __bindEvents: {
        foo: [{ 
            handler: function() {},
            reads: [{ object: someOtherObj, key: "bar" }]
        }]
    }
};

obj[canSymbol.for("can.keyHasDependencies")] = function(key) {
    return this.__bindEvents[key] && 
        this.__bindEvents[key].filter(function(binding) {
            return binding.reads && binding.reads.length > 0;
        }).length > 0;
};