TypeScript 5.6 Is a Game-Changer

The TypeScript team has unveiled the beta version of TypeScript 5.6, and it’s brimming with features designed to make our lives easier.

Catching Logical Errors Early: Disallowed Nullish and Truthy Checks

One of the standout features in TypeScript 5.6 is the stricter handling of nullish and truthy checks. Previously, TypeScript would quietly accept certain logical errors, leading to potential bugs that were hard to catch. Now, the compiler flags expressions that always evaluate to a specific boolean value, such as:

if (inputString => "hello") {
    // This condition is always true, but it's likely a mistake.
}

These stricter checks help catch logical errors early, making your code more robust and less prone to subtle bugs. It’s like having an extra pair of eyes scrutinising your logic, ensuring you don’t overlook potential issues.

Making Iterators More Powerful: Iterator Helper Methods

Iterators in JavaScript are great, but wouldn’t it be fantastic if they had the same handy methods as arrays? TypeScript 5.6 brings iterator helper methods, so now you can do things like this:

function* generateNumbers() {
    let num = 1;
    while (true) {
        yield num++;
    }
}

const squaredNumbers = generateNumbers().map(n => n * n);
console.log([...squaredNumbers.take(5)]); // Outputs: [1, 4, 9, 16, 25]

These methods make working with iterators as intuitive as working with arrays, simplifying complex operations and making your code cleaner and more readable.

Ensuring Type Safety: Strict Builtin Iterator Checks

TypeScript 5.6 introduces the BuiltinIterator type and the --strictBuiltinIteratorReturn flag to enforce stricter checks on iterators:

class NumberStream extends Iterator<number> {
    next() {
        return { value: Math.random(), done: false };
    }
}

const numbers = new NumberStream().map(n => n * 2);
console.log(numbers.next().value); // Outputs a random number multiplied by 2

This enhances type safety, reducing the risk of runtime errors and ensuring that your iterators behave as expected.

Embracing Flexibility: Arbitrary Module Identifiers

Ever wanted to use quirky module names but found it challenging? TypeScript 5.6 makes it possible:

export { default as "🔑" } from "./keyModule";

import { "🔑" as key } from "./keyModule";
key.doSomething();

This feature allows for better interoperability with other languages and tools, making TypeScript more versatile in different environments, including WebAssembly.

Catching Typos in Imports: The –noUncheckedSideEffectImports Option

TypeScript 5.6 introduces the --noUncheckedSideEffectImports option to catch typos and unexpected behavior in side-effect imports:

import "nonexistent-module"; // This will now throw an error if the module doesn't exist.

This option ensures that your imports are intentional and correct, preventing subtle bugs caused by unnoticed typos.

Speeding Up Development: The –noCheck Option

For those times when you need faster builds, TypeScript 5.6 offers the --noCheck option to skip type checking:

tsc --noCheck

This can significantly speed up your development process, allowing you to iterate faster by separating type checking from code emission.

Better Project Management: Allow –build with Intermediate Errors

In larger projects, TypeScript 5.6 allows the --build mode to continue even if there are errors in dependencies:

This enables developers to work on different parts of a project simultaneously without being blocked by upstream errors, improving productivity and flexibility in large codebases.

Faster Feedback in Editors: Region-Prioritized Diagnostics

TypeScript 5.6 introduces region-prioritised diagnostics, providing quicker feedback for the part of the code you’re currently working on.

This makes the editing experience smoother, especially in large files, as you get immediate feedback on your changes without waiting for the entire file to be checked.

Smarter Configuration Management: Search Ancestor Configuration Files

TypeScript 5.6 enhances how editors find the relevant tsconfig.json file, allowing more flexibility in project organisation:

This simplifies project setup and maintenance, making it easier to manage large and complex codebases.

Notable Behavioural Changes

Several noteworthy changes and bug fixes are included in TypeScript 5.6, such as always writing the .tsbuildinfo file and respecting file extensions and package.json configurations within node_modules.

These changes enhance the overall stability and predictability of the TypeScript compiler, ensuring smoother upgrades and fewer surprises during development.

Conclusion

TypeScript 5.6 is more than just an update; it’s a substantial improvement in making our development processes smoother, faster, and more reliable. From stricter type checks and enhanced iterator methods to faster build processes and better editor support, TypeScript 5.6 is set to make a significant impact on our coding experience.