Top 3 features in Typescript 5.5
Tags: webdev, typescript, news, beginners
Published: 2024-07-04 09:30:25

TypeScript has long been a favorite among developers for its ability to add static typing to JavaScript, enhancing code quality and developer productivity. With each new release, TypeScript continues to evolve, introducing features that simplify development and reduce potential errors. The latest version, TypeScript 5.5, is no exception. This version brings a host of new features and improvements designed to make coding in TypeScript even more efficient and enjoyable. In this blog post, we will explore the top three features of TypeScript 5.5: **better type inference**, **enhanced regular expression syntax checking**, and **new ECMAScript Set methods**. These enhancements underscore TypeScript’s commitment to providing a robust, scalable, and high-performance development experience.

## 1. Better Type Inference

TypeScript 5.5 brings significant improvements to type inference, making the code more robust and reducing the need for explicit type annotations.

### Improved Inference with filter method

TypeScript now better understands the results of filtering operations, making the types more precise and safe.

*Previous (typescript 5.4)*

![typescript 5.4 filter method](https://dev-to-uploads.s3.amazonaws.com/uploads/articles/vxnxzp0fhzqkfk8z614g.png)

*New (typescript 5.5)*

![typescript 5.5 filter method](https://dev-to-uploads.s3.amazonaws.com/uploads/articles/qemk5a6xjsrj8r9s9kky.png)

In this example, previously typescript was not good enough to infer that after filtering out null values `nums` only contains numbers but typeScript 5.5 correctly infers this. [Microsoft devblogs(inferred type predicates)](https://devblogs.microsoft.com/typescript/announcing-typescript-5-5/#inferred-type-predicates)

### Enhanced Control Flow Analysis

TypeScript is now able to narrow expressions of the form `obj[key]` when both `obj` and `key` are effectively constant. This enhancement reduces runtime errors and makes the code easier to maintain.

*Previous (typescript 5.4)*

![typescript 5.4 control flow](https://dev-to-uploads.s3.amazonaws.com/uploads/articles/ffdmdidaw13l2ytm62ha.png)

*New (typescript 5.5)*

![typescript 5.5 control flow](https://dev-to-uploads.s3.amazonaws.com/uploads/articles/0xzs2kdv8s5frkhqwxm1.png)

In the above example, neither `obj` nor `key` are ever mutated, so TypeScript can narrow the type of `obj[key]` to string in `if` block after the typeof check and to `Array<number>` in `else` block which previously it was unable to do so. [Microsoft devblogs(control flow narrowing)](https://devblogs.microsoft.com/typescript/announcing-typescript-5-5/#control-flow-narrowing-for-constant-indexed-accesses)

## 2. Enhanced Regular Expression Syntax Checking

Regular expressions are now subject to basic syntax checks in typescript 5.5. This enhancement helps catch common issues that were previously overlooked, ensuring that regular expressions adhere to ECMAScript standards. [Microsoft devblogs(enhanced regex)](https://devblogs.microsoft.com/typescript/announcing-typescript-5-5/#regular-expression-syntax-checking)

*Previous (typescript 5.4)*

![typescript 5.4 regex checks](https://dev-to-uploads.s3.amazonaws.com/uploads/articles/3o6vkclk6zezakxov8hk.png)

*New (typescript 5.5)*

![typescript 5.5 regex checks](https://dev-to-uploads.s3.amazonaws.com/uploads/articles/437tder2by4hg4tjssrs.png)

## 3. New ECMAScript Set Methods

TypeScript 5.5 introduces new `Set` methods that provide more robust ways to manipulate `sets`. Some of these methods, like `union`, `intersection`, `difference`, and `symmetricDifference`, take another `Set` and return a new `Set` as the result.mThe other methods, `sSubsetOf`, `isSupersetOf`, and `isDisjointFrom`, take another `Set` and return a `boolean`. [Microsoft devblogs(new set methods)](https://devblogs.microsoft.com/typescript/announcing-typescript-5-5/#support-for-new-ecmascript-set-methods)

Here's an example on how to use some of these methods.

```ts
let fruits = new Set(["apples", "bananas", "pears", "oranges"]);
let applesAndBananas = new Set(["apples", "bananas"]);
let applesAndOranges = new Set(["apples", "oranges"]);
let oranges = new Set(["oranges"]);
let emptySet = new Set();

////
// union
////

// Set(4) {'apples', 'bananas', 'pears', 'oranges'}
console.log(fruits.union(oranges));

// Set(3) {'apples', 'bananas', 'oranges'}
console.log(applesAndBananas.union(oranges));

////
// intersection
////

// Set(2) {'apples', 'bananas'}
console.log(fruits.intersection(applesAndBananas));

// Set(0) {}
console.log(applesAndBananas.intersection(oranges));

// Set(1) {'apples'}
console.log(applesAndBananas.intersection(applesAndOranges));

////
// difference
////

// Set(3) {'apples', 'bananas', 'pears'}
console.log(fruits.difference(oranges));

// Set(2) {'pears', 'oranges'}
console.log(fruits.difference(applesAndBananas));

// Set(1) {'bananas'}
console.log(applesAndBananas.difference(applesAndOranges));

////
// symmetricDifference
////

// Set(2) {'bananas', 'oranges'}
console.log(applesAndBananas.symmetricDifference(applesAndOranges)); // no apples

////
// isDisjointFrom
////

// true
console.log(applesAndBananas.isDisjointFrom(oranges));

// false
console.log(applesAndBananas.isDisjointFrom(applesAndOranges));

// true
console.log(fruits.isDisjointFrom(emptySet));

// true
console.log(emptySet.isDisjointFrom(emptySet));

////
// isSubsetOf
////

// true
console.log(applesAndBananas.isSubsetOf(fruits));

// false
console.log(fruits.isSubsetOf(applesAndBananas));

// false
console.log(applesAndBananas.isSubsetOf(oranges));

// true
console.log(fruits.isSubsetOf(fruits));

// true
console.log(emptySet.isSubsetOf(fruits));

////
// isSupersetOf
////

// true
console.log(fruits.isSupersetOf(applesAndBananas));

// false
console.log(applesAndBananas.isSupersetOf(fruits));

// false
console.log(applesAndBananas.isSupersetOf(oranges));

// true
console.log(fruits.isSupersetOf(fruits));

// false
console.log(emptySet.isSupersetOf(fruits));
```

Thank you for reading! I hope you found these new TypeScript 5.5 features as exciting as I do. 🎉 Happy coding! 🧑‍💻🚀