Many programming languages have one “non-value” called <code>null</code>. It indicates that a variable does not currently point to an object – for example, when it hasn’t been initialized yet.
In contrast, JavaScript has two such non-values: <code>undefined</code> and <code>null</code>. In this blog post, we examine how they differ and how to best use or avoid them.

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<code>undefined</code> vs. <code>null</code> revisited

<a href="https://github.com/tc39/proposal-import-assertions">The ECMAScript proposal “Import assertions”</a> (by Myles Borins, Sven Sauleau, Dan Clark, and Daniel Ehrenberg) introduces syntax for associating metadata with import statements. In this blog post, we examine what that looks like and why it’s useful.

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ECMAScript proposal: Import assertions

This blog post compares four ways of looping over Arrays:
<ul>
<li>
The <code>for</code> loop:
<pre><code class="language-js">for (let index=0; index &lt; someArray.length; index++) {
 const elem = someArray[index];
 // ···
}
</code></pre>
</li>
<li>
The <code>for-in</code> loop:
<pre><code class="language-js">for (const key in someArray) {
 console.log(key);
}
</code></pre>
</li>
<li>
The Array method <code>.forEach()</code>:
<pre><code class="language-js">someArray.forEach((elem, index) =&gt; {
 console.log(elem, index);
});
</code></pre>
</li>
<li>
The <code>for-of</code> loop:
<pre><code class="language-js">for (const elem of someArray) {
 console.log(elem);
}
</code></pre>
</li>
</ul>
<code>for-of</code> is often the best choice. We’ll see why.

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2ality

`undefined` vs. `null` revisited

ECMAScript proposal: Import assertions

Looping over Arrays: `for` vs. `for-in` vs. `.forEach()` vs. `for-of`