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react-native-polyfill

Overview

Some JS engines that are targeted by React Native, particularly iOS 8 and, to a lesser extent, Android 6, are missing some of the new ES2015 functions and they may not be polyfilled by a typical build system.

This leads to errors that look like this:

Unhandled JS Exception: undefined is not a function (evaluating ‘Number.parseInt’)

A lot of these functions are the ones that existed in prior versions of JavaScript but were added to the Number object to namespace them. For example:

parseInt('20', 10); // existing JavaScript function
Number.parseInt('20', 10); // the 'new' way of accessing the same function as of ES2015

Installing

npm install --save react-native-polyfill

To use the entire package and mutate the base objects, simply import or require the package:

import 'react-native-polyfill';
require('react-native-polyfill');

If you only want the Array or Number polyfills, you can include just one:

import 'react-native-polyfill/src/Array';
require('react-native-polyfill/src/Array');

If you just want a single function or you want to limit the number of changes to the base object, you can access the functions directly:

const includes = require('react-native-polyfill/src/Array/includes');

Methodology

Where available, this project has used the MDN polyfills or a close variation.

Warning

Importing this package into your project will mutate the prototype of JavaScript's base objects, if those objects do not already support the functionality. The decision to mutate these base objects in your code base should not be taken lightly. The polyfills in this package should be relatively low risk as they do not change prototypes in JavaScript engines that already implement the functions.

Polyfilled Functions

Array

  • includes

Number

  • isInteger
  • isNaN
  • isSafeInteger
  • parseFloat
  • parseInt

String

  • codePointAt
  • fromCodePoint
  • normalize // Uses the unorm library for a polyfill

Resources

More information about this topic can be found at: http://mcculloughwebservices.com/2016/11/29/adding-support-es2015-number-methods/