• Review the documentation: https://facebook.github.io/react-native
• Search for existing issues: https://github.com/facebook/react-native/issues
• Use the latest React Native release: https://github.com/facebook/react-native/releases

Environment

  React Native Environment Info:
    System:
      OS: Linux 4.17 Arch Linux rolling
      CPU: x64 Intel(R) Core(TM) i7-3770K CPU @ 3.50GHz
      Memory: 1.06 GB / 7.47 GB
      Shell: 5.5.1 - /bin/zsh
    Binaries:
      Node: 10.6.0 - /usr/bin/node
      Yarn: 1.7.0 - /usr/bin/yarn
      npm: 6.1.0 - /usr/bin/npm
      Watchman: 4.9.0 - /usr/bin/watchman
    SDKs:
      Android SDK:
        Build Tools: 23.0.1, 23.0.3, 25.0.2, 26.0.1, 26.0.2, 27.0.0, 27.0.3
        API Levels: 22, 23, 24, 25, 26, 27
    npmPackages:
      react: ^16.4.1 => 16.4.1 
      react-native: ^0.56.0 => 0.56.0 
    npmGlobalPackages:
      react-native-cli: 2.0.1
      react-native-git-upgrade: 0.2.7

Description

Bundler cuts off some used babel helpers in release build. Look like by mistake while optimization.
For example initializerDefineProperty and applyDecoratedDescriptor needed by @babel/proposal-decorators.

Reproducible Demo

{
  "presets": ["react-native"],
  "plugins": [
    ["@babel/proposal-decorators", {"legacy": true}]
  ]
}

"devDependencies": {
  "@babel/plugin-proposal-decorators": "7.0.0-beta.47"
}

function test() {}

class Test {
  @test val;
}

undefined is not a function (evaluating 'babelHelpers.applyDecoratedDescriptor(_class.prototype, "val", [test], {
    enumerable: true,
    initializer: null
  })')

Workaround 1 (can have side effects)

Be care because this workaround can bring some errors with external libs.

For RN 0.56:

yarn add --dev @babel/plugin-transform-runtime@7.0.0-beta.47

.babelrc

{
  "presets": ["react-native"],
  "plugins": [
    ["@babel/plugin-proposal-decorators", {"legacy": true}],
    ["@babel/plugin-transform-runtime", {
      "polyfill": false,
      "regenerator": false
    }]
  ]
}

For RN 0.57:

yarn add --dev @babel/plugin-transform-runtime@7.0.0

.babelrc

{
  "presets": ["module:metro-react-native-babel-preset"],
  "plugins": [
    ["@babel/plugin-proposal-decorators", {"legacy": true}],
    ["@babel/plugin-transform-runtime", {
      "polyfill": false,
      "regenerator": false
    }]
  ]
}

Workaround 2

Move app initialization to some other file (I'm using src/ dir for source) and update root index.js file.
N.B. require main app code instead of import because require executed after.

For RN 0.56:

yarn add @babel/runtime@7.0.0-beta.47

Root index.js

import applyDecoratedDescriptor from '@babel/runtime/helpers/es6/applyDecoratedDescriptor'
import initializerDefineProperty from '@babel/runtime/helpers/es6/initializerDefineProperty'

Object.assign(babelHelpers, {
  applyDecoratedDescriptor,
  initializerDefineProperty,
});

require('./src');

For RN 0.57:

yarn add @babel/runtime@7.0.0

Root index.js

import applyDecoratedDescriptor from '@babel/runtime/helpers/esm/applyDecoratedDescriptor'
import initializerDefineProperty from '@babel/runtime/helpers/esm/initializerDefineProperty'

Object.assign(babelHelpers, {
  applyDecoratedDescriptor,
  initializerDefineProperty,
});

require('./src');