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const person01 = {
  name: 'JM'
};

const person02 = person01;

/**
 * Mutating `person02` will cause effect also on `person01` because 
 * `person01` was assigned by reference not by value
 */

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let y = 3;

/**
 * The `sum` function is accessing the global variable `y` to compute for the sum
 */
const sum = (x) => x + y;

/**
 * Here we are mutating the state of the variable `y` to `6` 
 * which means that the computation of `sum` will now be different

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const sum = (x, y) => x + y;

/**
 * We are sure that `sum(3, 3)` will *always* return `6`
 * because the function `sum` is *pure*.
 * No matter how many times we call it with the same input,
 * it will produce the same output
 */
const six = sum(3, 3);

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import React, { useEffect } from 'react';

import {
  BrowserRouter as Router,
  Redirect,
  Route,
  Switch,
} from 'react-router-dom';

import './App.css';

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import { RouteProps } from 'react-router-dom';

import { GuardFunction } from '../types/guard';

import { tryCatchSync } from '../utils/tryCatch';

export type GuardFunctionArgs = RouteProps;
export type GuardFunction = (args: GuardFunctionArgs) => boolean;

type User = {

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import {
  Route,
  RouteProps,
  matchPath,
} from 'react-router-dom';

import { GuardFunction } from '../types/guard';

export type ProtectedRouteProps = RouteProps & {
  guards: GuardFunction[];

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import {
  format,
  isAfter,
  isSameDay,
} from 'date-fns';
import * as Yup from 'yup';

import { tryCatch } from '../../utils/tryCatch';

const validationSchema = Yup.object().shape({

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import { format } from 'date-fns';

export const post = async (req, res) => {
  const {
    body: {
      date: unformattedDate,
      startTime: unformattedStartTime,
      endTime: unformattedEndTime,
    },
  } = req;

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const getData = (id) => {
  if (!id) {
    throw new Error('No id found');
  }

  return [1, 2, 3, 4, 5].filter(i => i  % id);
};

const tryCatch = (tryer) => {
  try {

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// mutable variable

const getData = (id) => {
  if (!id) {
    throw new Error('No id found');
  }

  return [1, 2, 3, 4, 5].filter(i => i % id);
};