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TypeScript 3.7 Beta Is 'Feature-Complete'

TypeScript 3.7, with a new Beta, is now feature complete, with the dev team polishing it up in advance of the official release coming early next month.

In announcing the beta on Oct. 1, program manager Daniel Rosenwasser highlighted two features of special note in that they were highly requested by developers, and championed by the dev team for inclusion in TC39, a standardization effort for the vendor-neutral ECMAScript programming language, better known as JavaScript (which TypeScript enhances with features such as optional typing).

One of those is Optional Chaining, described by Rosenwasser as "one of the most highly-demanded ECMAScript features yet," which the dev team is heavily involved in progressing through the TC39 process.

"So what is optional chaining?" he said. "Well at its core, optional chaining lets us write code where we can immediately stop running some expressions if we run into a null or undefined. The star of the show in optional chaining is the new ?. operator for optional property accesses."

Closely related to that is the second upcoming ECMAScript feature Rosenwasser highlighted, also being championed by the dev team: the nullish coalescing operator.

"You can think of this feature -- the ?? operator -- as a way to “fall back” to a default value when dealing with null or undefined," Rosenwasser said.

So it can basically shorten up code like:

let x = (foo !== null && foo !== undefined) ?
    foo :
    bar();

to

let x = foo ?? bar();

Other features in the v3.7 beta highlighted by Rosenwasser include:

  • Assertion functions
  • Better support for never-returning functions
  • (More) recursive type aliases
  • --declaration and --allowJs
  • Build-free editing with project references
  • Uncalled function checks
  • // @ts-nocheck in TypeScript files
  • Semicolon formatter option

Once again, however, the Investigate error messages in haiku or iambic pentameter proposal that was added to the TypeScript roadmap in May 2018 was not mentioned in the v3.7 beta announcement post.

About the Author

David Ramel is an editor and writer for Converge360.

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