axeldelafosse / realm-js

Realm is a mobile database: an alternative to SQLite & key-value stores

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Realm is a mobile database that runs directly inside phones, tablets or wearables. This project hosts the JavaScript versions of Realm. Currently we support React Native (both iOS & Android), Node.js and Electron (on Windows, MacOS and Linux).


  • Mobile-first: Realm is the first database built from the ground up to run directly inside phones, tablets and wearables.
  • Simple: Data is directly exposed as objects and queryable by code, removing the need for ORM's riddled with performance & maintenance issues.
  • Modern: Realm supports relationships, generics, and vectorization.
  • Fast: Realm is faster than even raw SQLite on common operations, while maintaining an extremely rich feature set.

Getting Started

Please see the detailed instructions in our docs to use Realm JavaScript for node.js and Realm JavaScript for React Native. Please notice that currently only node.js version 10 or later (excluding 11) are supported.


Realm React Native and Node.js

The documentation can be found at The API reference is located at

Getting Help

  • Need help with your code?: Look for previous questions on the #realm tag — or ask a new question. You can also check out our Community Forum where general questions about how to do something can be discussed.
  • Have a bug to report? Open an issue. If possible, include the version of Realm, a full log, the Realm file, and a project that shows the issue.
  • Have a feature request? Open an issue. Tell us what the feature should do, and why you want the feature.

Building Realm

In case you don't want to use the precompiled version on npm, you can build Realm yourself from source. You’ll need an Internet connection the first time you build in order to download the core library.


  • Xcode 12+
  • node.js version 10.19 or later
  • nvm (on Mac and Linux)
  • cocoapods (on Mac)
  • Android SDK 23+
  • Android NDK 21.0
    • Available via the SDK Manager in Android Studio Tools > SDK Manager.
    • From the command-line: $ANDROID_SDK_ROOT/tools/bin/sdkmanager --install "ndk;21.0.6113669".
  • Android CMake
    • Available via the SDK Manager in Android Studio Tools > SDK Manager
    • From the command-line ```$ANDROID_SDK_ROOT/tools/bin/sdkmanager --install "cmake;3.18.1"````

Clone RealmJS repository:

git clone
cd realm-js
git submodule update --init --recursive

Note: On Windows the RealmJS repo should be cloned with symlinks enabled

#run in elevated command prompt
git clone -c core.symlinks=true

or manually create the symlinks using directory junctions if you already have the repo cloned.

#run in elevated command prompt
cd realm-js\react-native\android\src\main\jni
#remove src and vendor files
del src
del vendor
mklink /j "src" "../../../../../src/"
mklink /j "vendor" "../../../../../vendor"
cd realm-js\tests\react-test-app\android\app\src\main
#remove assets file
del assets
mklink /j assets "../../../../../data"

Note: If you have cloned the repo previously make sure you remove your node_modules directory since it may contain stale dependencies which may cause the build to fail.

Building for iOS:

  • Open react-native/ios/RealmReact.xcodeproj in Xcode
  • Select RealmReact under Targets
  • Build: ⌘ + B

Building for Android:

  • cd react-native/android
  • export ANDROID_NDK_HOME=$ANDROID_HOME/ndk/21.0.6113669 #Location for your NDK folder
  • ./gradlew publishAndroid
  • The compiled version of the Android module is here: <project-root>/android

Building for nodejs:

You can build for nodejs by running the command:

npm run build

If you want to build for Apple Silicon on an Intel based Mac, you can use the following command instead:

 npm run build-m1

Additional steps for Windows

On Windows you will need to setup the environment for node-gyp:

  • Option 1: Install windows-build-tools node package

    # run in elevated command prompt (as Administrator)
    npm install -g --production windows-build-tools
  • Option 2: Manually install and configure as described in the node-gyp manual.

    Note you may need to configure the build tools path using npm

    npm config set msbuild_path "C:\Program Files (x86)\Microsoft Visual Studio\2019\Community\MSBuild\Current\Bin\MSBuild.exe"

You also need to install openssl libraries with vcpkg:

git clone
cd vcpkg
vcpkg install openssl:x64-windows-static
mkdir C:\src\vcpkg\installed\x64-windows-static\lib
copy .\packages\openssl-windows_x64-windows-static\lib\libeay32.lib C:\src\vcpkg\installed\x64-windows-static\lib\
copy .\packages\openssl-windows_x64-windows-static\lib\ssleay32.lib C:\src\vcpkg\installed\x64-windows-static\lib

Installing the project's sub-packages

We've decided to slowly migrate this repository to a mono-repository containing multiple packages (stored in the ./packages directory), to install & link these, run

npx lerna bootstrap

Please familiarise yourself with Lerna to learn how to add dependencies to these packages.

Building docs

API documentation is written using JSDoc.

  • npm run jsdoc

The generated docs can be found by opening docs/output/realm/<version>/index.html.

Debugging the node addon

You can use Visual Studio Code to develop and debug. In the .vscode folder, configuration for building and debugging has been added for your convience.

VSCode has good support for debugging JavaScript, but to work with C++ code, you are required to install two additional VSCode extensions:

  • Microsoft C/C++
  • CodeLLDB

To begin, you will need to build the node addon and prepare the test environment:

npm install --build-from-source --debug
(cd tests && npm install)

Prior to begin debugging, you must start Realm Object Server. In VSCode, under menu Tasks/Run Task, find Download and Start Server.

In the debugging pane, you can find Debug LLDB + NodeJS in the dropdown. First select Start Debugging in the Debug menu.

Issues with debugging

Some users have reported the Chrome debugging being too slow to use after integrating Realm into their react-native project. This is due to the blocking nature of the RPC calls made through the Realm library. See realm#491 for more information. The best workaround is to use Safari instead, as a user has described here.

Running the tests

The tests will spawn a new shell when running, so you need to make sure that new shell instances use the correct version of npm. On Mac you can use Homebrew and you can add the following to your preferred shell setup:

export NVM_DIR="$HOME/.nvm"
. "$(brew --prefix nvm)/"

Install cocoapods

sudo gem install cocoapods

You can now use scripts/ to run the various tests. You will need yarn installed on the machine. options

  • eslint - lints the sources
  • react-tests - runs all React Native tests on iOS Simulator
  • react-tests-android runs all React Native Android tests on Android emulator
  • node - runs all tests for node
  • test-runners - checks supported tests runners are working correctly

If you modify or add a test, please remove tests/react-test-app/node_modules/realm-tests before running (of course, only if you are testing with React Native).

Testing on Windows

On Windows some of these targets are available as npm commands.

npm run eslint
npm run node-tests
npm run test-runners

Debugging the tests

You can attach a debugger to react-native tests by passing "Debug" to the script. A Chrome browser will open and connect to the react native application. Use the built-in Chrome Debugger to debug the code.

./scripts/ react-tests Debug

Using Visual Studio Code

You can debug node tests using Visual Studio Code. Just use one of the launch configurations.


Asynchronously submits install information to Realm.

Why are we doing this? In short, because it helps us build a better product for you. None of the data personally identifies you, your employer or your app, but it will help us understand what language you use, what Node.js versions you target, etc. Having this info will help prioritizing our time, adding new features and deprecating old features. Collecting an anonymized application path & anonymized machine identifier is the only way for us to count actual usage of the other metrics accurately. If we don’t have a way to deduplicate the info reported, it will be useless, as a single developer npm install-ing the same app 10 times would report 10 times more than another developer that only installs once, making the data all but useless. No one likes sharing data unless it’s necessary, we get it, and we’ve debated adding this for a long long time. If you truly, absolutely feel compelled to not send this data back to Realm, then you can set an env variable named REALM_DISABLE_ANALYTICS.

Currently the following information is reported:

  • What version of Realm is being installed.
  • The OS platform and version which is being used.
  • Node.js, v8, libuv, OpenSSL version numbers.
  • An anonymous machine identifier and hashed application path to aggregate the other information on.

Known issues

  • AWS Lambda is not supported.

Code of Conduct

This project adheres to the Contributor Covenant code of conduct. By participating, you are expected to uphold this code. Please report unacceptable behavior to


See for more details!


Realm JS and Realm Core are published under the Apache License 2.0.

This product is not being made available to any person located in Cuba, Iran, North Korea, Sudan, Syria or the Crimea region, or to any other person that is not eligible to receive the product under U.S. law.


If you use Realm and are happy with it, all we ask is that you please consider sending out a tweet mentioning @realm to share your thoughts

And if you don't like it, please let us know what you would like improved, so we can fix it!



Realm is a mobile database: an alternative to SQLite & key-value stores



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