JavaScript - Liberated functions - First Class Functions(Array, sort method, comparison function, descending order)

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 10.(Liberated functions - First Class Functions)の EXERCISE(No. 6850)を取り組んでみる。

EXERCISE(No. 6850)

コード(Emacs)

HTML5

<pre id="output0"></pre>
<button id="run0">run</button>
<button id="clear0">clear</button>
<script src="sample6.js"></script>

JavaScript

let btn0 = document.querySelector('#run0'),
    btn1 = document.querySelector('#clear0'),
    pre0 = document.querySelector('#output0'),
    p = (x) => pre0.textContent += x + '\n',
    range = (start, end, step=1) => {
        let result = [];
        for (let i = start; i < end; i += 1) {
            result.push(i);
        }
        return result;
    };

let compareNumbersDesc = (num1, num2) => {
    if (num2 > num1) {
        return 1;
    }
    if (num1 === num2) {
        return 0;
    }
    return -1;
};


let output = () => {
    let nums = range(0, 10).map(() => Math.floor(Math.random() * 20));

    p(nums);
    nums.sort(compareNumbersDesc);
    p(nums);
};

let clear = () => pre0.textContent = '';

btn0.onclick = output;
btn1.onclick = clear;

output();