TypeScript 4.3, the latest stable release of Microsoft’s typed superset of JavaScript, introduces significant updates aimed at improving the developer experience. One of the standout features of this version is the ability to specify types for both reading and writing to object properties. This enhancement is particularly useful for developers working with APIs that convert values in TypeScript, where there has traditionally been a trade-off between being “precise” and being “permissive.” Previously, developers had to choose between making reading values easier at the cost of writing them or vice versa. With TypeScript 4.3, it’s now possible to achieve more control over both operations, improving both code safety and usability.
Released on May 26, TypeScript 4.3 builds on earlier beta and release candidate versions. In addition to the new property type specification feature, it includes several other notable updates. One of these is the addition of the override keyword. This keyword ensures that any method marked with it will only be valid if a method with the same name exists in the superclass. This feature helps prevent errors such as accidentally missing a method when extending a class, which can be a common issue when overriding methods in JavaScript. To enforce this behavior, TypeScript also introduces a noImplicitOverride flag that will generate an error if a method is overridden without the explicit use of the override keyword.
Another major improvement in TypeScript 4.3 is the enhancement of template string types. The language now has better support for relating and inferring types across different template strings, making it easier for developers to ensure that their template strings match the intended types. TypeScript automatically performs checks to confirm whether each part of a template string can successfully match, reducing the chances of runtime errors due to mismatched types.
TypeScript 4.3 also introduces stronger encapsulation for class elements. In this version, developers can now assign private names to not only properties but also methods, accessors, and static members of classes. This feature makes it easier to enforce true privacy at runtime, ensuring that private members are not accessible or modifiable from outside the class. With these updates, TypeScript continues to enhance its ability to offer a more robust, type-safe environment for JavaScript development.