[modules][ios] Defer the creation of module's JS object until its fir…

…st usage (#18863)

packages/expo-modules-core/CHANGELOG.md

@@ -22,6 +22,7 @@
 - Automatically convert records to dicts when returned by the function. ([#18824](https://github.com/expo/expo/pull/18824) by [@tsapeta](https://github.com/tsapeta))
 - Closures passed to definition components are now implicitly capturing `self` on iOS. ([#18831](https://github.com/expo/expo/pull/18831) by [@tsapeta](https://github.com/tsapeta))
 - Support for CSS named colors in `UIColor` and `CGColor` convertibles on iOS. ([#18845](https://github.com/expo/expo/pull/18845) by [@tsapeta](https://github.com/tsapeta))
+- Lazy load building the module's JavaScript object from the definition on iOS (already implemented on Android). ([#18863](https://github.com/expo/expo/pull/18863) by [@tsapeta](https://github.com/tsapeta))
 
 ### 🐛 Bug fixes
 

packages/expo-modules-core/common/cpp/JSIUtils.cpp

@@ -0,0 +1,20 @@
+// Copyright 2022-present 650 Industries. All rights reserved.
+
+#include "JSIUtils.h"
+
+namespace expo {
+
+std::vector<jsi::PropNameID> jsiArrayToPropNameIdsVector(jsi::Runtime &runtime, const jsi::Array &array) {
+  size_t size = array.size(runtime);
+  std::vector<jsi::PropNameID> vector;
+
+  vector.reserve(size);
+
+  for (size_t i = 0; i < size; i++) {
+    jsi::String name = array.getValueAtIndex(runtime, i).getString(runtime);
+    vector.push_back(jsi::PropNameID::forString(runtime, name));
+  }
+  return vector;
+}
+
+} // namespace expo

packages/expo-modules-core/common/cpp/JSIUtils.h

@@ -0,0 +1,19 @@
+// Copyright 2022-present 650 Industries. All rights reserved.
+
+#pragma once
+#ifdef __cplusplus
+
+#include <jsi/jsi.h>
+
+namespace jsi = facebook::jsi;
+
+namespace expo {
+
+/**
+ Converts `jsi::Array` to a vector with prop name ids (`std::vector<jsi::PropNameID>`).
+ */
+std::vector<jsi::PropNameID> jsiArrayToPropNameIdsVector(jsi::Runtime &runtime, const jsi::Array &array);
+
+} // namespace expo
+
+#endif // __cplusplus

packages/expo-modules-core/common/cpp/LazyObject.cpp

@@ -0,0 +1,45 @@
+// Copyright 2022-present 650 Industries. All rights reserved.
+
+#include "JSIUtils.h"
+#include "LazyObject.h"
+
+namespace expo {
+
+LazyObject::LazyObject(const LazyObjectInitializer initializer) : initializer(initializer) {}
+
+LazyObject::~LazyObject() {
+  backedObject = nullptr;
+}
+
+jsi::Value LazyObject::get(jsi::Runtime &runtime, const jsi::PropNameID &name) {
+  if (!backedObject) {
+    if (name.utf8(runtime) == "$$typeof") {
+      // React Native asks for this property for some reason, we can just ignore it.
+      return jsi::Value::undefined();
+    }
+    backedObject = initializer(runtime);
+  }
+  return backedObject ? backedObject->getProperty(runtime, name) : jsi::Value::undefined();
+}
+
+void LazyObject::set(jsi::Runtime &runtime, const jsi::PropNameID &name, const jsi::Value &value) {
+  if (!backedObject) {
+    backedObject = initializer(runtime);
+  }
+  if (backedObject) {
+    backedObject->setProperty(runtime, name, value);
+  }
+}
+
+std::vector<jsi::PropNameID> LazyObject::getPropertyNames(jsi::Runtime &runtime) {
+  if (!backedObject) {
+    backedObject = initializer(runtime);
+  }
+  if (backedObject) {
+    jsi::Array propertyNames = backedObject->getPropertyNames(runtime);
+    return jsiArrayToPropNameIdsVector(runtime, propertyNames);
+  }
+  return {};
+}
+
+} // namespace expo

packages/expo-modules-core/common/cpp/LazyObject.h

@@ -0,0 +1,43 @@
+// Copyright 2022-present 650 Industries. All rights reserved.
+
+#pragma once
+
+#ifdef __cplusplus
+
+#include <jsi/jsi.h>
+
+namespace jsi = facebook::jsi;
+
+namespace expo {
+
+/**
+ A function that is responsible for initializing the backed object.
+ */
+typedef std::function<std::shared_ptr<jsi::Object>(jsi::Runtime &)> LazyObjectInitializer;
+
+/**
+ A host object that defers the creating of the raw object until any property is accessed for the first time.
+ */
+class JSI_EXPORT LazyObject : public jsi::HostObject {
+public:
+  using Shared = std::shared_ptr<LazyObject>;
+
+  LazyObject(const LazyObjectInitializer initializer);
+
+  virtual ~LazyObject();
+
+  jsi::Value get(jsi::Runtime &, const jsi::PropNameID &name) override;
+
+  void set(jsi::Runtime &, const jsi::PropNameID &name, const jsi::Value &value) override;
+
+  std::vector<jsi::PropNameID> getPropertyNames(jsi::Runtime &rt) override;
+
+private:
+  const LazyObjectInitializer initializer;
+  std::shared_ptr<jsi::Object> backedObject;
+
+}; // class LazyObject
+
+} // namespace expo
+
+#endif // __cplusplus

packages/expo-modules-core/ios/JSI/EXJSIInstaller.mm

@@ -3,6 +3,7 @@
 #import <ExpoModulesCore/EXJSIInstaller.h>
 #import <ExpoModulesCore/EXJavaScriptRuntime.h>
 #import <ExpoModulesCore/ExpoModulesHostObject.h>
+#import <ExpoModulesCore/LazyObject.h>
 #import <ExpoModulesCore/Swift.h>
 
 namespace jsi = facebook::jsi;

packages/expo-modules-core/ios/JSI/EXJavaScriptObject.h

@@ -42,6 +42,11 @@ NS_SWIFT_NAME(JavaScriptObject)
  Returns the pointer to the underlying object.
  */
 - (nonnull jsi::Object *)get;
+
+/**
+ Returns the shared pointer to the underlying object.
+ */
+- (std::shared_ptr<jsi::Object>)getShared;
 #endif // __cplusplus
 
 #pragma mark - Accessing object properties

packages/expo-modules-core/ios/JSI/EXJavaScriptObject.mm

@@ -37,6 +37,11 @@ - (nonnull instancetype)initWith:(std::shared_ptr<jsi::Object>)jsObjectPtr
   return _jsObjectPtr.get();
 }
 
+- (std::shared_ptr<jsi::Object>)getShared
+{
+  return _jsObjectPtr;
+}
+
 #pragma mark - Accessing object properties
 
 - (BOOL)hasProperty:(nonnull NSString *)name

packages/expo-modules-core/ios/JSI/ExpoModulesHostObject.h

@@ -3,6 +3,7 @@
 #ifdef __cplusplus
 
 #import <vector>
+#import <unordered_map>
 #import <jsi/jsi.h>
 
 namespace jsi = facebook::jsi;
@@ -11,6 +12,9 @@ namespace jsi = facebook::jsi;
 
 namespace expo {
 
+using SharedJSIObject = std::shared_ptr<jsi::Object>;
+using UniqueJSIObject = std::unique_ptr<jsi::Object>;
+
 class JSI_EXPORT ExpoModulesHostObject : public jsi::HostObject {
 public:
   ExpoModulesHostObject(EXAppContext *appContext);
@@ -25,6 +29,7 @@ class JSI_EXPORT ExpoModulesHostObject : public jsi::HostObject {
 
 private:
   EXAppContext *appContext;
+  std::unordered_map<std::string, UniqueJSIObject> modulesCache;
 
 }; // class ExpoModulesHostObject
 

packages/expo-modules-core/ios/JSI/ExpoModulesHostObject.mm

@@ -2,21 +2,40 @@
 
 #import <ExpoModulesCore/ExpoModulesHostObject.h>
 #import <ExpoModulesCore/EXJavaScriptObject.h>
+#import <ExpoModulesCore/LazyObject.h>
 #import <ExpoModulesCore/Swift.h>
 
 namespace expo {
 
 ExpoModulesHostObject::ExpoModulesHostObject(EXAppContext *appContext) : appContext(appContext) {}
 
 ExpoModulesHostObject::~ExpoModulesHostObject() {
+  modulesCache.clear();
   [appContext setRuntime:nil];
 }
 
 jsi::Value ExpoModulesHostObject::get(jsi::Runtime &runtime, const jsi::PropNameID &name) {
-  NSString *moduleName = [NSString stringWithUTF8String:name.utf8(runtime).c_str()];
-  EXJavaScriptObject *nativeObject = [appContext getNativeModuleObject:moduleName];
+  std::string moduleName = name.utf8(runtime);
+  NSString *nsModuleName = [NSString stringWithUTF8String:moduleName.c_str()];
 
-  return nativeObject ? jsi::Value(runtime, *[nativeObject get]) : jsi::Value::undefined();
+  if (![appContext hasModule:nsModuleName]) {
+    // The module object can already be cached but no longer registered — we remove it from the cache in that case.
+    modulesCache.erase(moduleName);
+    return jsi::Value::undefined();
+  }
+  if (UniqueJSIObject &cachedObject = modulesCache[moduleName]) {
+    return jsi::Value(runtime, *cachedObject);
+  }
+
+  // Create a lazy object for the specific module. It defers initialization of the final module object.
+  LazyObject::Shared moduleLazyObject = std::make_shared<LazyObject>(^SharedJSIObject(jsi::Runtime &runtime) {
+    return [[appContext getNativeModuleObject:nsModuleName] getShared];
+  });
+
+  // Save the module's lazy host object for later use.
+  modulesCache[moduleName] = std::make_unique<jsi::Object>(jsi::Object::createFromHostObject(runtime, moduleLazyObject));
+
+  return jsi::Value(runtime, *modulesCache[moduleName]);
 }
 
 void ExpoModulesHostObject::set(jsi::Runtime &runtime, const jsi::PropNameID &name, const jsi::Value &value) {

packages/expo-modules-core/ios/Swift/ModuleHolder.swift

@@ -101,6 +101,7 @@ public final class ModuleHolder {
     guard let runtime = appContext?.runtime else {
       return nil
     }
+    log.info("Creating JS object for module '\(name)'")
     return definition.build(inRuntime: runtime)
   }