feat: Add trim() func and size property

cpp/MmkvHostObject.cpp

@@ -372,6 +372,25 @@ jsi::Value MmkvHostObject::get(jsi::Runtime& runtime, const jsi::PropNameID& pro
           return jsi::Value::undefined();
         });
   }
+
+  if (propName == "trim") {
+    // MMKV.trim()
+    return jsi::Function::createFromHostFunction(
+        runtime, jsi::PropNameID::forAscii(runtime, funcName),
+        0,
+        [this](jsi::Runtime& runtime, const jsi::Value& thisValue, const jsi::Value* arguments,
+               size_t count) -> jsi::Value {
+           instance->trim();
+
+          return jsi::Value::undefined();
+        });
+  }
+
+  if (propName == "size") {
+    // MMKV.size
+    size_t size = instance->actualSize();
+    return jsi::Value(static_cast<int>(size));
+  }
 
   return jsi::Value::undefined();
 }

example/src/App.tsx

@@ -5,6 +5,10 @@ import { MMKV, useMMKVString } from 'react-native-mmkv';
 
 const storage = new MMKV();
 
+storage.addOnValueChangedListener((key) => {
+  console.log(`${key} changed! New size: ${storage.size}`);
+});
+
 export default function App() {
   const [text, setText] = React.useState<string>('');
   const [key, setKey] = React.useState<string>('');

src/MMKV.ts

@@ -1,3 +1,4 @@
+import { AppState } from 'react-native';
 import { createMMKV } from './createMMKV';
 import { createMockMMKV } from './createMMKV.mock';
 import { isJest } from './PlatformChecker';
@@ -106,6 +107,20 @@ interface MMKVInterface {
    * Encryption keys can have a maximum length of 16 bytes.
    */
   recrypt: (key: string | undefined) => void;
+  /**
+   * Trims the storage space and clears memory cache.
+   *
+   * Since MMKV does not resize itself after deleting keys, you can call `trim()`
+   * after deleting a bunch of keys to manually trim the memory- and
+   * disk-file to reduce storage and memory usage.
+   *
+   * In most applications, this is not needed at all.
+   */
+  trim(): void;
+  /**
+   * Get the current total size of the storage, in bytes.
+   */
+  readonly size: number;
   /**
    * Adds a value changed listener. The Listener will be called whenever any value
    * in this storage instance changes (set or delete).
@@ -129,6 +144,8 @@ export type NativeMMKV = Pick<
   | 'getBuffer'
   | 'set'
   | 'recrypt'
+  | 'trim'
+  | 'size'
 >;
 
 const onValueChangedListeners = new Map<string, ((key: string) => void)[]>();
@@ -151,6 +168,11 @@ export class MMKV implements MMKVInterface {
       ? createMockMMKV()
       : createMMKV(configuration);
     this.functionCache = {};
+
+    const weakSelf = new WeakRef(this);
+    AppState.addEventListener('memoryWarning', () => {
+      weakSelf.deref()?.trim();
+    });
   }
 
   private get onValueChangedListeners() {
@@ -179,6 +201,9 @@ export class MMKV implements MMKVInterface {
     }
   }
 
+  get size(): number {
+    return this.nativeInstance.size;
+  }
   set(key: string, value: boolean | string | number | ArrayBuffer): void {
     const func = this.getFunctionFromCache('set');
     func(key, value);
@@ -227,6 +252,10 @@ export class MMKV implements MMKVInterface {
     const func = this.getFunctionFromCache('recrypt');
     return func(key);
   }
+  trim(): void {
+    const func = this.getFunctionFromCache('trim');
+    func();
+  }
 
   toString(): string {
     return `MMKV (${this.id}): [${this.getAllKeys().join(', ')}]`;