shouldCompactOnLaunch is passed the used bytes, not unused bytes

CHANGELOG.md

@@ -14,7 +14,7 @@ X.Y.Z Release notes
   `shouldCompactOnLaunch` config property for them.
 
 ### Bug fixes
-* None.
+* Fix incorrect documentation of the `shouldCompactOnLaunch` parameters.
 
 ### Internals
 * None.

docs/realm.js

@@ -324,7 +324,7 @@ class Realm {
  *   a Realm for the first time during the life of a process to determine if it should be compacted
  *   before being returned to the user. The function takes two arguments:
  *     - `totalSize` - The total file size (data + free space)
- *     - `unusedSize` - The total bytes used by data in the file.
+ *     - `usedSize` - The total bytes used by data in the file.
  *   It returns `true` to indicate that an attempt to compact the file should be made. The compaction
  *   will be skipped if another process is accessing it.
  * @property {string} [path={@link Realm.defaultPath}] - The path to the file where the

src/js_realm.hpp

@@ -518,10 +518,10 @@ void RealmClass<T>::constructor(ContextType ctx, ObjectType this_object, size_t
                 }
 
                 FunctionType should_compact_on_launch_function = Value::validated_to_function(ctx, compact_value, "shouldCompactOnLaunch");
-                config.should_compact_on_launch_function = [=](uint64_t total_bytes, uint64_t unused_bytes) {
+                config.should_compact_on_launch_function = [=](uint64_t total_bytes, uint64_t used_bytes) {
                     ValueType arguments[2] = {
                         Value::from_number(ctx, total_bytes),
-                        Value::from_number(ctx, unused_bytes)
+                        Value::from_number(ctx, used_bytes)
                     };
 
                     ValueType should_compact = Function<T>::callback(ctx, should_compact_on_launch_function, this_object, 2, arguments);