Updates from the 89th TC39 meeting

There were several items on the agenda, this post focuses on feature proposals and their progress from the meeting that was held between March 28th-31st, 2022.

Stage 1:

• Type Annotations: Enable developers to add type annotations.

• Function once: Standardize once function in the language core.

Stage 2:

• Decorator metadata: Decorators can associate metadata with the value that is being decorated. (P.S: The repo shall be updated with content.)

Stage 3:

• RegExp set notation + properties of strings: extend the syntax for character classes to add support for set difference/subtraction, set intersection, and nested character classes.

• Change array by copy: Provides additional methods on Array.prototype and TypedArray.prototype to enable changes on the array by returning a new copy of it with the change.

• Decorators (sans metadata): Functions called on classes, class elements, or other JavaScript syntax forms during definition.

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@gnumanth

Comments

[Ken Bellows]

Disappointed not to see Record & Tuple advanced, that's my most anticipated proposal at the moment. Can't wait for comparison-by-value of complex objects!

[Jon Rimmer]

Pattern matching didn't get to accepted for stage 2? ☹️

[Conan]

Yeah, fingers-cross for future meetings on that one! If it's of any interest I wrote a pattern-matching library after initially learning about the TC39 proposal, trying to shoe-horn it into looking a little like the spec with varying degrees of success.