JavaScript continues to evolve rapidly, driven by the work of TC39 and active contributors like the Deno team. At the recent 108th TC39 meeting, nine proposals moved forward across stages — from early concepts (Stage 0) to fully standardized features (Stage 4).
Here’s an overview of what’s coming soon, what’s experimental, and how these changes might impact the way we write JavaScript.
Stage 4: Ready for Use
Explicit Resource Management (using)
JavaScript is finally getting deterministic resource cleanup through the new using keyword (and its async variant await using). Inspired by C# and Python, this feature ensures resources like files or sockets are properly released when leaving a block of code.
Objects can implement [Symbol.dispose]() or [Symbol.asyncDispose]() methods, which are called automatically.
class FileHandle {
constructor(name) {
this.name = name; // open file...
}
[Symbol.dispose]() {
console.log(`${this.name} closed`);
}
}
function readFile() {
{
using file = new FileHandle("data.txt");
// File operations...
}
// file.[Symbol.dispose]() is automatically called here
}
✅ Already supported in Chrome 134, Firefox 134, and Deno v2.3.
In Deno, this applies to resources like Deno.File and Deno.Conn. Example:
using server = Deno.serve({ port: 8000 }, () => {
return new Response("Hello, world!");
});
const response = await fetch("http://localhost:8000");
console.log(await response.text()); // "Hello, world!"
// server stops automatically
The Deno team also proposes extending using to simplify async context propagation (tracing, logging, spans).
Array.fromAsync
Like Array.from, but works with async iterables and returns a Promise that resolves to an array.
async function* generate() {
yield await Promise.resolve(1);
yield await Promise.resolve(2);
}
const nums = await Array.fromAsync(generate());
console.log(nums); // [1, 2]
✅ Supported in all browsers, Deno v1.38, and Node.js v22.
Error.isError
A new reliable way to detect errors across realms or inheritance.
Error.isError(new TypeError("oops")); // true
Error.isError({ name: "TypeError", message: "oops" }); // false
✅ Supported in all browsers and Deno v2.2.
Stage 3: Candidate Features
Immutable ArrayBuffer
Introduces transferToImmutable() and sliceToImmutable() for safe, immutable binary data.
let buf = new ArrayBuffer(100);
let imm = buf.transferToImmutable();
console.log(buf.byteLength, imm.byteLength); // 0, 100
imm[0] = 1; // ❌ TypeError
Useful for multi-threading, workers, and binary APIs like Deno.writeFile() without unnecessary copies.
Stage 2: Drafts
Random.Seeded
Deterministic randomness with reproducible sequences.
const prng = new Random.Seeded(42);
console.log(prng.random()); // same sequence every run
Great for simulations, games, and tests.
Number.prototype.clamp
A clean alternative to Math.min(Math.max(x, min), max).
(5).clamp(0, 10); // 5
(-5).clamp(0, 10); // 0
(15).clamp(0, 10); // 10
Stage 1: Early Proposals
Trailing Zeros in Intl.NumberFormat
New option trailingZeroDisplay for cleaner number formatting.
new Intl.NumberFormat("en", {
minimumFractionDigits: 2,
trailingZeroDisplay: "auto"
}).format(1.5); // "1.50"
new Intl.NumberFormat("en", {
trailingZeroDisplay: "stripIfInteger"
}).format(2); // "2"
Comparisons
A standardized way to generate diff-like outputs for values, useful for testing frameworks and logging.
Random Namespace
Convenient helpers for numbers, arrays, and sampling.
Random.int(-5, 5); // -1
Random.sample(["A", "B"]); // "B"
Random.shuffle([1,2,3]); // [3,1,2]
What’s Next
JavaScript’s evolution is far from slowing down. TC39 is shaping the language for modern use cases: async workflows, safer data handling, reproducibility, and developer ergonomics.
Deno remains a strong advocate of these changes, integrating them early to showcase their real-world benefits. The next TC39 meeting is scheduled for late September, where discussions on these proposals will continue.
🔗 Sources: