Typescript 3.3 is finally released!

After releasing TypeScript 3.3 RC, two weeks ago, yesterday Microsoft announced the availability of TypeScript 3.3. TypeScript 3.3 contains no breaking changes and is a comparatively smaller release than usual.

What’s new in Typescript 3.3

Better behavior when calling union types

When there is a union type A | B, TypeScript now allows users to access all of the properties common to both A and B. For example, the intersection of members. You can get a property from a union type only if it’s known to be present in every union type. When every type has only one signature with identical parameters, things work. Such a restriction was too much and have errors in some areas. So, in TypeScript 3.3, the following code as shown in the blog will work:

type Fruit = "apple" | "orange";

type Color = "red" | "orange";

type FruitEater = (fruit: Fruit) => number;     // eats and ranks the fruit

type ColorConsumer = (color: Color) => string;  // consumes and describes the colors

declare let f: FruitEater | ColorConsumer;

f("orange"); // It works! Returns a 'number | string'.

f("apple");  // error - Argument of type '"apple"' is not assignable to parameter of type '"orange"'.

f("red");    // error - Argument of type '"red"' is not assignable to parameter of type '"orange"'.

The parameters of the above signatures are ‘intersected’ to create a new signature. When the impossible intersections are gone, what remains is “orange” & “orange” which is just “orange”. That is not to say there are no restrictions. The new behavior is active only when only one type in the union has multiple overloads and a generic signature. The forEach method will now be callable, but there may be some issues under noImplicitAny.

--build --watch use incremental file watching

In TypeScript 3.3, --build mode’s --watch flag leverage incremental file watching. This results in significantly faster builds with a reduction of 50% to 75% in build times of the original --build --watch times.

Sublime Text supports JavaScript editing

The TypeScript plugin for Sublime Text now supports editing in JavaScript files. Users will now get more accurate completions, rename, go-to-definition, and more in JavaScript code that utilizes JSDoc and interoperates with TypeScript code.

Typescript recently announced the ‘TypeScript Roadmap’ for January 2019- June 2019 which outlines the priorities that the team will be focussing on, over the next 6 months.

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