string `startsWith` produces false negatives

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Environment

Environment:
  OS: Linux 4.9
  Node: 8.11.2
  Yarn: 1.6.0
  npm: 5.6.0
  Watchman: Not Found
  Xcode: N/A
  Android Studio: Not Found

Packages: (wanted => installed)
  react: 16.3.1 => 16.3.1
  react-native: ~0.55.2 => 0.55.4

Description

I have a component that was filtering a list of suggestions, and I stumbled on a strange bug. The list was mysteriously not including some items it should have, and I eventually figured out that the Javascript engine was producing incorrect results on strings that had UTF8 characters in them. That is, someString.startsWith(someOtherString) was producing false when it shouldn’t have.

Steps to Reproduce

console.log('mother'.startsWith('m'));
console.log('mother\'s'.startsWith('m'));
console.log('mother’s'.startsWith('m'));

Note the Unicode apostrophe in the last case.

If it makes a difference, I used create-react-native-app to bootstrap my app, and I’m running it in Expo.

Expected Behavior

true
true
true

Actual Behavior

true
true
false

[armadillojim]

@MrPluto and @dmaksimovic, React Native 0.56, 0.57, and 0.58 all continued to use the same JSC. They finally updated it, though. See https://github.com/facebook/react-native/issues/19737#issuecomment-454205028

I double checked, and you can see the change live now in 0.59. https://github.com/facebook/react-native/blob/0.58-stable/ReactAndroid/build.gradle#L148 shows the old JSC, and https://github.com/facebook/react-native/blob/0.59-stable/ReactAndroid/build.gradle#L136 is now evergreen.

I haven’t tried upgrading yet myself, but it seems that should fix this issue.

[arthakdoo]

const text = 'abcde 😎';   // note the emoji

text.startsWith('abc'); // <-- returns false (incorrect)
text.indexOf('abc'); // <-- returns zero (correct)

Node: 8.12.0 React: 16.8.2 React Native: 0.57.8 @babel/core: 7.3.3 @babel/preset-env: 7.3.1 @babel/preset-react: 7.0.0 Platform: Android