各言語特有っぽい構文: JavaScript/TypeScript

// JavaScript - 分割代入 + スプレッド合成 (while版)
const binarySearch = (arr, target) => {
  let { left, right } = { left: 0, right: arr.length - 1 };

  while (left <= right) {
    const mid = (left + right) >>> 1;
    const value = arr.at(mid) ?? undefined;

    if (value === target) return mid;

    ({ left, right } = value < target
      ? { left: mid + 1, right }
      : { left, right: mid - 1 });
  }
  return -1;
};

console.log(binarySearch([1, 3, 5, 7, 9], 5)); // 2

// TypeScript - ジェネリクス + 再帰 + スプレッド合成
type Range = { left: number; right: number };

const binarySearch = <T>(arr: T[], target: T): number => {
  const search = ({ left, right }: Range): number => {
    if (left > right) return -1;
    const mid = (left + right) >>> 1;
    const value = arr.at(mid);
    if (value === target) return mid;
    return search(
      value! < target
        ? { ...{ left, right }, left: mid + 1 }
        : { ...{ left, right }, right: mid - 1 }
    );
  };
  return search({ left: 0, right: arr.length - 1 });
};

console.log(binarySearch([1, 3, 5, 7, 9], 5)); // 2

const obj = { key1: value1, key2: value2 }
type ObjType = { key1: Type1; key2: Type2 } // TS

// 短くかける, 式を返せる
const binarySearch = (arr, target) => { ... }

// 同等
function binarySearch(arr, target) { ... } // this がある

// 値も返せる
const sum = (a, b) => a + b
const merge = (obj1, obj2) => ({ ...obj1, ...obj2 }) 

// フィールド取り出し
const { left, right } = state
// 引数も分割代入可能
const area = ({ left, right }) => {}
// オブジェクト合成
{ ...state, left: mid + 1 }
const newState = { ...oldState, key: newValue }
const { a, b, ...rest } = obj
// with assign
const { a: alpha, b: beta } = obj
const area = ({ left: l, right: r }) => {}
const { size: { w, h: height }} = rect

null ?? 'default' // 'default'
undefined ?? 'default' // 'default'
0 ?? 'default' // 0
'' ?? 'default' // ''

const swap = <T, S>(t: T, s: S): [S, T] => [s, t]