HTML5 - Storing Things Locally: Web Storage(JSON(parse method, stringify method), localStorage, setItem, getItem)

Head First HTML5 Programming

開発環境

• macOS Sierra - Apple (OS)
• Emacs (Text Editor)
• Safari(Web browser)

Head First HTML5 Programming (Elisabeth Robson (著)、Eric Freeman (著)、O'Reilly Media)の Chapter 9.(Storing Things Locally: Web Storage)、EXERCISE(No. 6639) を取り組んでみる。

EXERCISE(No. 6639)

コード(Emacs)

HTML5

<pre id="output0"></pre>
<input id="note_text" type="text">
<button id="add_button">Add Sticky Note to Self</button>
<br>
<button id="run0">run</button>
<button id="clear0">clear</button>

<script src="sample2.js"></script>

JavaScript

let btn0 = document.querySelector('#run0'),
    btn1 = document.querySelector('#clear0'),
    btn2 = document.querySelector('#add_button'),
    input0 = document.querySelector('#note_text'),
    pre0 = document.querySelector('#output0'),
    p = (x) => pre0.textContent += x + '\n';

let createSticky = () => {
    let value = input0.value,
        key = `sticky_${localStorage.length}`;

    localStorage.setItem(key, value);

    let stickiesArray = localStorage['stickiesArray'];
    if (stickiesArray) {
        stickiesArray = JSON.parse(stickiesArray);
    } else {
        stickiesArray = [];
        localStorage.setItem('stickiesArray', JSON.stringify(stickiesArray));
    }
    stickiesArray.push(key);
    localStorage.setItem('stickiesArray', JSON.stringify(stickiesArray));
};

btn2.onclick = createSticky;

let init = () => {

    let stickiesArray = localStorage['stickiesArray'];

    if (stickiesArray) {
        stickiesArray = JSON.parse(stickiesArray);
    } else {
        stickiesArray = [];
        localStorage.setItem('stickiesArray', JSON.stringify(stickiesArray));
    }
    stickiesArray.forEach((key) => {
        let value = localStorage[key];
        p(value);
    });
};
let output = () => {
    init();
};

btn0.onclick = output;
btn1.onclick = () => pre0.textContent = '';

output();