Everything in Dart is an Object.

class Object {
 /**
  * Creates a new [Object] instance.
  *
  * [Object] instances have no meaningful state, and are only useful
  * through their identity. An [Object] instance is equal to itself
  * only.
  */
 const Object();

 /**
  * The equality operator.
  *
  * The default behavior for all [Object]s is to return true if and
  * only if [:this:] and [other] are the same object.
  *
  * If a subclass overrides the equality operator it should override
  * the [hashCode] method as well to maintain consistency.
  */
 bool operator ==(other) => identical(this, other);

 /**
  * Get a hash code for this object.
  *
  * All objects have hash codes. Hash codes are guaranteed to be the
  * same for objects that are equal when compared using the equality
  * operator [:==:]. Other than that there are no guarantees about
  * the hash codes. They will not be consistent between runs and
  * there are no distribution guarantees.
  *
  * If a subclass overrides [hashCode] it should override the
  * equality operator as well to maintain consistency.
  */
 external int get hashCode;

 /**
  * Returns a string representation of this object.
  */
 external String toString();

 /**
  * [noSuchMethod] is invoked when users invoke a non-existant method
  * on an object. The name of the method and the arguments of the
  * invocation are passed to [noSuchMethod] in an [Invocation].
  * If [noSuchMethod] returns a value, that value becomes the result of
  * the original invocation.
  *
  * The default behavior of [noSuchMethod] is to throw a
  * [noSuchMethodError].
  */
 external dynamic noSuchMethod(Invocation invocation);

 /**
  * A representation of the runtime type of the object.
  */
 external Type get runtimeType;
}