TypeScript - Functions - small typesafe assertion library, generic

Programming TypeScript
Making Your JavaScript Applications Scale
楽天ブックス 紀伊國屋書店

開発環境

• macOS Mojave - Apple (OS)
• Windows 10 Pro (OS)
• Visual Studio Code (Text Editor)
• TypeScript (プログラミング言語)
• Node.js(JavaScriptの実行環境)

Programming TypeScript: Making Your JavaScript Applications Scale (Boris Cherny(著)、O'Reilly Media)のChapter 4(Functions)、Exercises(82)5の解答を求めてみる。

コード

TypeScript

type Is =  <T>(a:T, b:T) => boolean
let is:Is = (a, b) => a === b

function is1<T>(a:T, b:T) {
    return a == b
}
let pairs = [['string', 'otherstring'],
             [true, false],
             [42, 42]]

pairs.forEach(([a, b]) => console.log(a, b, is(a, b), is1(a, b)))

console.log('[Hard]')
let is2 = <T>(...args:T[]): boolean => {
    let len = args.length
    if (len === 0) {
        return true
    }
    let first = args[0]
    for (let index = 1; index < len; index++) {
        if (args[index] !== first) {
            return false
        }
    }
    return true
}

console.log(is2([1], [1,2], [1,2,3]))
console.log(is2(1, 1, 1, 1, 1))

入出力結果(Bash、cmd.exe(コマンドプロンプト)、Terminal)

$ ts-node sample5.ts 
string otherstring false false
true false false false
42 42 true true
[Hard]
false
true
$