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5-2 Iterator - My Frontend Note
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<h1>5-2 Iterator</h1>
<div class="read-more clearfix">
<span class="date">2016/11/14</span>
<span>posted in </span>
<span class="posted-in"><a href='ES2015.html'>ES2015</a></span>
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<blockquote>
<p>本文為 <strong><a href="https://www.codeschool.com/courses/es2015-the-shape-of-javascript-to-come">ES2015: The Shape of JavaScript to Come</a></strong>（CodeSchool）線上課程筆記</p>
</blockquote>
<p><strong>本文目錄：</strong></p>
<ul>
<li>
<a href="#toc_0">怎麼讓 objects 變得 iterable</a>
</li>
<li>
<a href="#toc_1">變成 iterable 可以幹嘛？</a>
</li>
</ul>
<span id="more"></span><!-- more -->
<p><strong>Iterables</strong> are <strong>objects</strong> that know how to return a special objects called an <strong>iterator</strong>.</p>
<p><strong>Iterator</strong> is an object that knows how to access items from a collection one at a time, while keeping track of its current position within the sequence.</p>
<p><strong>Iterables</strong> return an <strong>iterator</strong> object. This object </p>
<p>重要</p>
<h3 id="toc_0">怎麼讓 objects 變得 iterable</h3>
<p>An iterator is an object with a <code>next</code> property, returned by the result of calling the <code>Symbol.iterator</code> method</p>
<p>An iterator is an object with a <code>next</code> property, returned by a function assigned to the <code>Symbol.iterator</code> property</p>
<pre><code class="language-js">let post = {
title: "New Features in JS",
replies: 19
};
post[Symbol.iterator] = function() {
let properties = Object.keys(this);
let count = 0;
let isDone = false;
let next = () => {
if(count>= properties.length) {
isDone = true;
}
return { done: isDone, value: this[properties[count++]] }
// this -> post object
// count++ -> increments count after it's read
return { next }; // <= iterator object
};
</code></pre>
<h3 id="toc_1">變成 iterable 可以幹嘛？</h3>
<p><strong>for...of</strong></p>
<pre><code class="language-js">for (let p of post) {
console.log(p);
}
// > "New Features in JS"
// > 19
</code></pre>
<p><strong>spread operator</strong></p>
<pre><code class="language-js">let values = [...post];
console.log(values);
// > ['New Features in JS', 19]
</code></pre>
<p><strong>destructuring</strong></p>
<pre><code class="language-js">let [title, replies] = post;
console.log(title);
console.log(replies);
// > 'New Features in JS'
// > 19
</code></pre>
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title="Previous Post: [Error] Git Precommit Lint Failed at Tower: "env: node: No such file or directory" （on Mac OS）">« [Error] Git Precommit Lint Failed at Tower: "env: node: No such file or directory" （on Mac OS）</a>
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