JavaScript ES12 (2021)

ECMAScript 2021, or JavaScript ES12, introduced a set of small but powerful features that improve developer experience, especially in areas like string manipulation, object handling, Promise debugging, and logical operations.

In this tutorial, you’ll learn:

1. Overview of ES12
2. Key features with examples
3. A code model project using ES12 features

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🔍 What’s New in ES12 (2021)?

The ES12 update includes:

• Logical Assignment Operators (||=, &&=, ??=)
• Numeric Separators
• String.prototype.replaceAll()
• Promise any()
• WeakRef and FinalizationRegistry
• Object.hasOwn()

Let’s break them down.

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1. ✅ Logical Assignment Operators (||=, &&=, ??=)

These are shorthand ways of combining logic and assignment.

🧪 Examples:

javascriptCopyEditlet name = null;
name ||= "Guest";       // name = "Guest"

let count = 5;
count &&= 10;           // count = 10

let title = undefined;
title ??= "Untitled";   // title = "Untitled"

This simplifies conditionally setting variables.

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2. 🔢 Numeric Separators (_)

You can use underscores (_) to make large numbers more readable.

javascriptCopyEditconst billion = 1_000_000_000;
console.log(billion); // 1000000000

This does not affect the value—just the readability.

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3. 🔁 String.prototype.replaceAll()

Replaces all instances of a substring without needing regex with global flag.

javascriptCopyEditconst text = "apple, banana, apple";
const updated = text.replaceAll("apple", "orange");
console.log(updated); // "orange, banana, orange"

This is more intuitive than using text.replace(/apple/g, 'orange').

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4. 🔂 Promise.any()

Returns the first fulfilled promise. If all reject, it returns an AggregateError.

javascriptCopyEditconst p1 = Promise.reject("Fail 1");
const p2 = Promise.resolve("Success");
const p3 = Promise.reject("Fail 2");

Promise.any([p1, p2, p3]).then(result => {
  console.log(result); // "Success"
});

Perfect when you want any successful result from multiple sources.

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5. 🧼 Object.hasOwn() (Better than hasOwnProperty())

Checks if an object has a direct property of its own.

javascriptCopyEditconst user = { name: "Alice" };
console.log(Object.hasOwn(user, "name")); // true

It’s more reliable than using hasOwnProperty because it works even if the object doesn’t inherit from Object.prototype.

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6. 🧠 WeakRef and FinalizationRegistry (Advanced)

These deal with memory management and garbage collection.

javascriptCopyEditlet obj = { name: "data" };
let ref = new WeakRef(obj);

// Later: you can dereference the weak reference
console.log(ref.deref()); // { name: "data" }

Useful for building caches or observers, but not often needed in everyday projects.

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🛠 Code Model: Post Processor Tool

🎯 Objective:

• Set default metadata with logical assignment
• Replace all keywords in post content
• Check if post has certain data
• Format large view counts
• Resolve any available translations using Promise.any()

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✅ ES12 Code Example:

javascriptCopyEdit// Initial post object
let post = {
  title: undefined,
  content: "Learn JS. JS is fun!",
  views: 25_000,
  tags: null,
};

// Logical assignment to set defaults
post.title ??= "Untitled Post";
post.tags ||= ["javascript", "tutorial"];

// Replace all mentions of "JS" with "JavaScript"
post.content = post.content.replaceAll("JS", "JavaScript");

// Display view count using numeric separator
console.log(`Views: ${post.views}`);

// Check if property exists
if (Object.hasOwn(post, "title")) {
  console.log("Title exists:", post.title);
}

// Simulate translations loading
const en = Promise.reject("No English");
const es = Promise.resolve("Artículo en Español");
const fr = Promise.reject("Aucun Français");

Promise.any([en, es, fr])
  .then(translation => {
    console.log("Translation loaded:", translation);
  })
  .catch(error => {
    console.log("No translations available:", error);
  });

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🖥 Output:

yamlCopyEditViews: 25000
Title exists: Untitled Post
Translation loaded: Artículo en Español

This project uses:

• ??=, ||= for safe default values
• replaceAll() for content replacement
• Object.hasOwn() for safety checking
• Promise.any() for loading available translations
• 25_000 for improved readability with numeric separators

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🧠 Summary Table

Feature	Description	Example
??=, `		=, &&=`
Numeric separators	Makes large numbers readable	1_000_000
replaceAll()	Replace all substrings in a string	"a a".replaceAll("a", "b")
Promise.any()	Returns first fulfilled Promise	Promise.any([...])
Object.hasOwn()	Checks direct object property	Object.hasOwn(obj, 'key')
WeakRef	Weak reference to an object	new WeakRef(obj)

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✅ Conclusion

JavaScript ES12 (2021) focused on ergonomics — making common tasks easier, safer, and more readable. Whether you’re assigning default values, working with promises, or processing strings, these features simplify your code and reduce boilerplate.

Even if you’re a beginner, features like ??=, replaceAll(), and Promise.any() are quick wins for writing cleaner, modern JavaScript.