kwoncharles

function MyComponent() {
  const [alphabet, set] = useState('A');
  const prevAlphabet = usePrevious(alphabet);
  
  useEffect(() => {
    if (alphabet === 'C' && prevAlphabet === 'B') {
       doSomething();
    }
  }, [alphabet]);
  // ..

kwoncharles

import { useEffect, useRef } from 'react';

function usePrevious(value) {
  const ref = useRef();

  useEffect(() => {
    ref.current = value;
  }, [value]); 

  return ref.current;

kwoncharles

import { useState, useCallback, useRef } from 'react';
import { removeNonNumeric, parseNumWithMaxValue } from '@/utils/StringUtils';

interface Options {
  initialValue?: string;
  maxValue?: number;
  minValue?: number;
  maxLength?: number;
  minLength?: number;
  autoFix?: boolean;

kwoncharles

import React from 'react';
import Helmet from 'react-helmet'; 

function My() {
  
  return (
    <>
      <Helmet>
        <title>My page</title>
        <meta property="description" content="discover yourself" />

kwoncharles

#[derive(Debug)]
struct Currency {
    currency_symbol: char,
    exchange_rate: i32
}

impl Currency {
    fn to_won(&self, amount: i32) -> i32 {
        self.exchange_rate * amount
    } 

kwoncharles

impl Currency {
    fn to_won(&mut self, amount: i32) -> i32 {
        self.exchange_rate = 1200;
        self.exchange_rate * amount
    }
}

fn main() {
    let dollar: Currency = Currency {
        currency_symbol: '$',

kwoncharles

fn main() {
    let reference_to_nothing = dangle();
}

fn dangle() -> &String {
    let s = String::from("hello");

    &s
}

kwoncharles

fn main() {
    let mut s = String::from("hello");

    change(&mut s);
}

fn change(some_string: &mut String) {
    some_string.push_str(", world");
}

kwoncharles

fn main() {
    let s = String::from("hello");
    change(&s);
}

fn change(some_string: &String) {
    some_string.push_str(", world");
}

kwoncharles

fn main() {
    let s1 = String::from("hello");

    let len = calculate_length(&s1);

    println!("The length of '{}' is {}.", s1, len);
}

fn calculate_length(s: &String) -> usize {
    s.len()