jsc-android

What is jsc-android?

The jsc-android package provides an optimized version of the JavaScriptCore engine for Android. This allows developers to leverage the latest JavaScript features and improvements in performance within their React Native applications or any other Android project that requires an embedded JavaScript engine.

What are jsc-android's main functionalities?

Using modern JavaScript features in Android apps

This code demonstrates how to use jsc-android to run JavaScript code, utilizing modern JavaScript features, directly within an Android application. It creates a new JavaScript context and evaluates a simple script.

"import org.liquidplayer.javascript.JSContext;\n\npublic class MainActivity extends AppCompatActivity {\n    @Override\n    protected void onCreate(Bundle savedInstanceState) {\n        super.onCreate(savedInstanceState);\n        setContentView(R.layout.activity_main);\n\n        JSContext context = new JSContext();\n        context.evaluateScript(\"'Hello, World!'.toUpperCase();\");\n    }\n}"

Improving React Native performance

By including jsc-android in a React Native project's dependencies, developers can improve the performance of their applications. This is particularly beneficial for complex applications that require a lot of JavaScript execution.

"dependencies {\n    implementation 'org.webkit:android-jsc:r250230'\n}\n"

Other packages similar to jsc-android

v8-android

Similar to jsc-android, v8-android provides the V8 JavaScript engine for Android applications. While jsc-android uses the JavaScriptCore engine, v8-android uses Google's V8 engine. This difference in the underlying engine can lead to variations in performance and compatibility with JavaScript features.

hermes-engine

Hermes is a JavaScript engine optimized for running React Native on Android. It aims to improve startup time, decrease memory usage, and increase overall performance. Unlike jsc-android, Hermes is built specifically for React Native and may offer better optimizations for React Native apps.

README

JSC build scripts for Android

The aim of this project is to provide maintainable build scripts for the JavaScriptCore JavaScript engine and allow the React Native community to incorporate up-to-date releases of JSC into the framework on Android.

This project is based on facebook/android-jsc but instead of rewriting JSC's build scripts into BUCK files, it relies on CMake build scripts maintained in a GTK branch of WebKit maintained by the WebKitGTK team (great work btw!). Thanks to that, with just a small amount of work we should be able to build not only current but also future releases of JSC. An obvious benefit for everyone using React Native is that this will allow us to update JSC for React Native on Android much more often than before (note that facebook/android-jsc uses JSC version from Nov 2014), which is especially helpful since React Native on iOS uses the built-in copy of JSC that is updated with each major iOS release (see this as a reference).

Requirements

There is a huge list of requirements that need to be installed on your system in order to be able to cross-compile JSC for Android. To simplify the process of setting up the environment we provide a Docker image that comes with everything you will need. If you decide to use our Docker image, the only thing you need to do is to prefix each command with this:

docker run -v `pwd`:/bitrise/src --rm swmansion/jsc-android-buildscripts

Example:

docker run -v `pwd`:/bitrise/src --rm swmansion/jsc-android-buildscripts ./fetch_sources.sh

Don't want to use Docker

As mentioned the list of dependencies is huge, we tried to list everything that is needed below:

• Android SDK & NDK
• Ruby (2.3), Python (2.7), Node (7.x), Git, SVN, gperf
• CMake installed via Android SDK manager

Build instructions

IMPORTANT: Remember to prefix each command with the appropriate Docker command given above when using our Docker image

1. git clone https://github.com/SoftwareMansion/jsc-android-buildscripts.git .
2. ./fetch_sources.sh
3. ./icu-prep.sh
4. ./jsc-prep.sh
5. ./all.sh
6. ./gradlew lib:installArchives libIntl:installArchives (add -w /bitrise/src/lib to docker run args)

The Maven repo containing the android-jsc AAR will be available at ./lib/android.

Distribution

JSC library built using this project is distributed over npm: npm/jsc-android. The library is packaged as a local Maven repository containing AAR files that include the binaries. Please refer to the section below in order to learn how your app can consume this format.

How to use it with my React Native app

Follow steps below in order for your React Native app to use new version of JSC VM on android:

1. Add jsc-android to the "dependencies" section in your package.json:

dependencies {
+  "jsc-android": "^216113.0.0",

then run npm install or yarn (depending which npm client you use) in order for the new dependency to be installed in node_modules

1. Modify andorid/build.gradle file to add new local maven repository packaged in the jsc-android package to the search path:

allprojects {
    repositories {
        mavenLocal()
        jcenter()
        maven {
            // All of React Native (JS, Obj-C sources, Android binaries) is installed from npm
            url "$rootDir/../node_modules/react-native/android"
        }
+       maven {
+           // Local Maven repo containing AARs with JSC library built for Android
+           url "$rootDir/../node_modules/jsc-android/android"
+       }
    }
}

1. Update your app's build.gradle file located in android/app/build.gradle to force app builds to use new version of the JSC library as opposed to the version specified in react-native gradle module as a dependency:

}

+configurations.all {
+    resolutionStrategy {
+        force 'org.webkit:android-jsc:r216113'
+    }
+}

dependencies {
    compile fileTree(dir: "libs", include: ["*.jar"])

1. You're done, rebuild your app and enjoy updated version of JSC on android!

Testing

As a part of this project we provide a patch to the React Native source code that allows for measuring a React Native application's cold-start. The methodology behind this test is to modify the part of the code that is responsible for loading JS bundles into the JS VM such that we measure and store the execution time, and to modify the process of instantiating the bridge so we can run it multiple times. To learn more about how the perf tests work and how to perform them, refer to this document. Results for the Samsung Galaxy S4 are presented below, cold start has been measured on rather large React Native app with minified bundle of size at around 3M:

	android-jsc (r174650)	new JSC (r216113)
cold start time	2530 ms	2150 ms (-15%)
binary size (armv7)	1.8 MiB	4.3 MiB
binary size (x86)	4.4 MiB	7.4 MiB
binary size (arm64)	N/A	6.5 MiB
binary size (x86_64)	N/A	7.2 MiB

International variant

Starting with 216113.0.0 version, we provide two build variants which differ in i18n support.

Default variant

By default we ship with no international support. Methods like Date.toLocaleString will act as Date.toString. String.localeCompare will just compare each character's byte value.

International variant

International variant includes ICU i18n library and necessary data allowing to use e.g. Date.toLocaleString and String.localeCompare that give correct results when using with locales other than en-US. Note that this variant is about 6MiB larger per architecture than default.

To use this variant instead replace patch from the third installation step with:

}

+configurations.all {
+    resolutionStrategy {
+        eachDependency { DependencyResolveDetails details ->
+            if (details.requested.name == 'android-jsc') {
+                details.useTarget group: details.requested.group, name: 'android-jsc-intl', version: 'r216113'
+            }
+        }
+    }
+}

dependencies {
    compile fileTree(dir: "libs", include: ["*.jar"])

Note that using variant with i18n support will have some significant impact on the binary size as the ICU library will need to be distributed along with ICU-data library which contains data helpful with localizing numbers/dates/collation/etc for all possible locales. Here is the summary of all the libraries sizes (including JSC) when using i18n variant.

	new JSC intl variant (r216113)
binary size (armv7)	11.2 MiB
binary size (x86)	15.6 MiB
binary size (arm64)	14.4 MiB
binary size (x86_64)	15.2 MiB

Credits

This project has been built in cooperation between Expo.io and Software Mansion