Microsoft official blog announcement 　US Microsoft officially released “TypeScript 4.0” on August 20 (local time). Currently available from package management systems such as “NuGet” and “npm”. Extensions and plugins for “Visual Studio” and code editors have also been released. 　”TypeScript” is an open source programming language developed by Microsoft. It is a superset of statically typed functions added to “JavaScript” and is suitable for applications such as large-scale development where “JavaScript” has been weak. The deliverables have a mechanism to be transpiled (converted) to “JavaScript” and executed, and it is also attractive that it can be widely used in environments that support “JavaScript” such as Web browsers and “Node.js”. The QA site familiar to developers, “StackOverflow” is the second most beloved language (1st is “Rust”), and about 89% of developers want to use it again in the “The State of JavaScript” survey. I am very satisfied with the answer.

　The latest version, “TypeScript 4.0,” has no major changes, and is the culmination of improvements since “TypeScript 3.0” released in July 2018 . Sample code and learning resources are available, so it’s a good opportunity for beginners who want to get started with TypeScript. The main changes since “TypeScript 3.0” are as follows.

• TypeScript 3.1: “Mapped types” function extended for tuples and arrays (Mapped Tuple Type)
• TypeScript 3.2: Focus on improving stability. Strict typing of bind, call and apply methods with “–strictBindCallApply” option
• TypeScript 3.3: Continued focus on stability. Add file incremental build in “–build” mode
• TypeScript 3.4: “readonly” related enhancements. Shorter build time with “–incremental” flag
• TypeScript 3.5/3.6: Add smarter compatibility checking rules
• TypeScript 3.7: Corresponding to “Optional Chaining” and “Nullish Coalescing”, it is possible to write “foo?.bar()” and “let x = foo ?? bar”. Notable release with many improvements, including support for “Assertion Functions” and “Recursive Type Aliases”
• TypeScript 3.8/3.9: Introducing type-only import/export, in addition to ECMAScript features such as private fields, top-level weights in modules, new export syntax. Performance and scalability are also optimized

　In addition, “TypeScript 4.0” includes “Variadic Tuple Types”, “Labeled Tuple Elements”, “unknown” in “catch” clause, three new assignment operators (a && b, a || b, a ?? b). Is supported, and the support function of the code editor is enhanced. The supported editors are “Visual Studio 2017”, “Visual Studio 2019” and “Visual Studio Code Insider”.