JavaScript - Handling events - Asynchronous Coding(event object (for DOM events), properties)

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 WHO DOES WHAT?(No. 5911)を取り組んでみる。

WHO DOES WHAT?(No. 5911)

コード(Emacs)

HTML5

<pre id="output0"></pre>
<button id="run0">run</button>
<button id="clear0">clear</button>

<script src="sample1.js"></script>

JavaScript

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

let b0 = document.querySelector('body');

b0.onclick = (event) => {
    for (let prop in event) {
        p(`${prop}: ${event[prop]}`);
    }
    p(
        ['target', 'type', 'timeStamp', 'clientX', 'clientY', 'touches']
            .map((prop) => `event['${prop}'] = ${event[prop]}`)
            .join('\n')
    );
};

let output = () => {
    b0.click(); 
};

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

output();