obaranovskyi

type PredicateFn = (value: any, index?: number) => boolean;
type ProjectionFn = (value: any, index?: number) => any;

function or(...predicates: PredicateFn[]): PredicateFn {
  return (value) => predicates.some((predicate) => predicate(value));
}

function and(...predicates: PredicateFn[]): PredicateFn {
  return (value) => predicates.every((predicate) => predicate(value));
}

rafaelpadovani

import React, {forwardRef, useRef, useState, useImperativeHandle} from 'react';
import {View, Animated, Text, StatusBar, StyleSheet} from 'react-native';

const Toast = forwardRef((props, ref) => {
    const animatedValue = useRef(new Animated.Value(0)).current;
    const [modalShown, setModalShown] = useState(false);
    const [message, setMessage] = useState('Success!');
    const [toastColor, setToastColor] = useState('green');
    const [textColor, setTextColor] = useState('black');

karol-majewski

/**
 * Challenge: given a list of icon names, find icons that exist in sizes 16x16px *and* 24x24px.
 * This is an AND relationship, not an OR relationship.
 * 
 * The solution should be: '16-hamburger' | '16-warning' | '24-hamburger' | '24-warning'.
 */
type IconName =
  | '16-hamburger' // 👈🏻
  | '16-warning'   // 👈🏻
  | '16-foo'

FeMaffezzolli

/**
 * Creates a flatten object from an any level nested object.
 *
 * @example
 *
 * Create following object:
 *
 * {
 *    'address.city.name': 'São Paulo',
 *    'address.state.name': 'SP',

mikaello

Group array of JavaScript objects by keys

This fork of JamieMason's implementation changes the key parameter to be an array of keys instead of just a single key. This makes it possible to group by multiple properties instead of just one.

Implementation

const groupBy = keys => array =>
  array.reduce((objectsByKeyValue, obj) => {
    const value = keys.map(key => obj[key]).join('-');

cameronblandford

// Because we're using an ORM (Objection), it's a pain to add a tsvector when inserting, 
// since tsvectors and FTS aren't supported by Objection. Instead, I've added a hook that 
// fires on insert which auto-generates the tsvector field for each newly inserted entry. 
// This is an example knex migration file for said behavior.

const addUserIndex = `
ALTER TABLE public.user ADD "document" tsvector;

CREATE FUNCTION my_trigger_function()
RETURNS trigger AS $$

harish2704

/* Implementation of lodash.get function */
function getProp( object, keys, defaultVal ){
  keys = Array.isArray( keys )? keys : keys.split('.');
  object = object[keys[0]];
  if( object && keys.length>1 ){
    return getProp( object, keys.slice(1) );
  }
  return object === undefined? defaultVal : object;
}

jherax

type FilterOperator = 'AND' | 'OR';
type FiltersBy<T> = {
  [K in keyof T]?: (value: T[K]) => boolean;
};

/**
 * Factory function that creates a specialized function to filter
 * arrays, by validating all filters (AND operator),
 * or validating just one of the filters (OR operator).
 * @param operator Method to validate all filters: AND, OR

andymatuschak

A composable pattern for pure state machines with effects

State machines are everywhere in interactive systems, but they're rarely defined clearly and explicitly. Given some big blob of code including implicit state machines, which transitions are possible and under what conditions? What effects take place on what transitions?

There are existing design patterns for state machines, but all the patterns I've seen complect side effects with the structure of the state machine itself. Instances of these patterns are difficult to test without mocking, and they end up with more dependencies. Worse, the classic patterns compose poorly: hierarchical state machines are typically not straightforward extensions. The functional programming world has solutions, but they don't transpose neatly enough to be broadly usable in mainstream languages.

Here I present a composable pattern for pure state machiness with effects,

sethlopezme

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