JavaScript - Handling events - Asynchronous Coding(Timer, setInterval, clearInterval)

Head First JavaScript Programming

開発環境

• macOS Sierra - Apple (OS)
• Emacs (Text Editor)
• JavaScript (プログラミング言語)
• Safari(Web browser)

Head First JavaScript Programming (Eric T. Freeman (著)、Elisabeth Robson (著)、O'Reilly Media)の Chapter 9.(Handling events - Asynchronous Coding)の EXERCISE(No. 6055)を取り組んでみる。

EXERCISE(No. 6055)

コード(Emacs)

HTML5

<pre id="output0"></pre>
<button id="run0">run</button>
<button id="clear0">clear</button>
<script src="sample3.js"></script>

JavaScript

let btn0 = document.querySelector('#run0'),
    btn1 = document.querySelector('#clear0'),
    pre0 = document.querySelector('#output0'),
    p = (x) => pre0.textContent += x + '\n';


let tm;
let output = () => {
    let tick = true;
    tm = setInterval(() => {
        if (tick) {
            p('Tick');
            tick = false;
        } else {
            p('Tock');
            tick = true;
        }
    }, 1000);
};

let clear = () => {
    clearInterval(tm);
    pre0.textContent = '';
};
btn0.onclick = output;
btn1.onclick = clear;

output();