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RN Coding Snippets / stuff one might need one day

Android

Reading from the default shared preferences file

// requires access to the activity
val sharedPreferencesFile = activity?.get()?.let {
 it.getSharedPreferences("${it.packageName}_preferences", Context.MODE_PRIVATE)

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const padArrayEnd = <T>(arr: T[], targetLength: number, val: T): T[] => {
  if (arr.length >= targetLength) return [...arr]
  return arr.concat(Array(targetLength - arr.length).fill(val))
}

console.log(padArrayEnd(["0", "1"], 3, ""))
console.log(padArrayEnd(["0", "1", "2"], 3, ""))
console.log(padArrayEnd(["0", "1", "2", "3"], 3, ""))

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import React from 'react';
import { NavigationStackScreenProps } from 'react-navigation-stack';

interface Props extends NavigationStackScreenProps {
  foo: string;
}
const TestScreen = ({ navigation, foo }: Props) => {
  const barDirectly = navigation.getParam('bar');

  return <Text>bar from navigation: {barDirectly} bar as foo from HOC: {foo}</Text>;

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What helped me to get everything running on my Apple Macbook with the M1 chip:

• Check first that your terminal is running on the arm64-architecture by running uname -m. If it’s x86_64, you’re running on Rosetta (see https://earthly.dev/blog/using-apple-silicon-m1-as-a-cloud-engineer-two-months-in/)
• Follow the normal environment setup guide from React Native
• Follow this answer from Stackoverflow when installing Cocoapods
• Run pod install in your iOS-folder, everything should be working flawless :)

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import { combineReducers, Action } from '@reduxjs/toolkit';

const withClearStateOnAction = <S = any>(clearStateAction: Action) => (
  reducer: Reducer<S | undefined, Action>,
) => (state: S, action: Action) => {
  if (clearStateAction.type === action.type) {
    return reducer(undefined, clearStateAction);
  }
  return reducer(state, action);
};

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iOS / Mac

List all devices & simulators available on your Mac:

xcrun simctl list devices available

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command line tools for working with images to json

Extract all exif data as list into a json file:

exiftool -j -q dir > data.json

Sort the exif data by the original creation time:

jq 'sort_by(.DateTimeOriginal)' data.json

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Density	Android density qualifier	iOS scaling factor
Low-density (~120dpi)	ldpi	not supported
Medium-density (~160dpi)	mdpi	original scale
High-density (~240dpi)	hdpi	not supported
Extra-high-density (~320dpi)	xhdpi	@2x
Extra-extra-high-density (~480dpi)	xxhdpi	@3x
Extra-extra-extra-high-density (~640dpi)	xxxhdpi	@4x

source: https://developer.android.com/studio/write/resource-manager#automatic-parsing

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/**
 * Curried higher-order function taking a predicate and an actual resolver function. In case the
 * predicate returns true, an empty list is returned, otherwise the result of the actual resolver function.
 *
 * Both the predicate and the resolver function will get the all arguments as a standard resolver function.
 */
const condResolveEmptyList = predicate => resolver => (
  data,
  args,
  context,

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const { performance } = require('perf_hooks');
const express = require('express');

const expressRequestDurationMiddleware = (req, res, next) => {
  performance.mark('request.start');
  
  const end = res.end;
  res.end = (...args) => {
    performance.mark('request.end');