TypeScript News Wednesday, July 18

Microsoft/TypeScript

  • The following code is a compiler error under as of #24013: – – It may be fulfilled with any type (eg, or ), so it was incorrect to allow.
  • For example, this type is a weak type: – – In TypeScript 2.4, it’s now an error to assign anything to a weak type when there’s no overlap in properties.
  • As an example of a new errors you might spot as a result: – – TypeScript’s checking of callback parameters is now covariant with respect to immediate signature checks.
  • TypeScript still isn’t able to infer the type argument, so to fix this you have to provide the type argument yourself: – – This requirement helps find errors in the body of the promise code.
  • Alternatively, you can either specify an explicit type annotation on the callback argument: – – Mostly, this should catch errors that were previously allowed as valid comma expressions.

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Microsoft/TypeScript

Microsoft/TypeScript

  • This system is different than the type system employed by some other popular languages you may have used (e.g. Java, C#, etc.) – – The idea behind structural typing is that two types are compatible if their members are compatible.
  • In TypeScript, this is not the case – a with at least as many members (with appropriate types) as is a subtype of regardless of explicit heritage.
  • In summary, in the TypeScript type system, the question of whether a more-specific-type-accepting function should be assignable to a function accepting a less-specific type provides a prerequisite answer to whether an array of that more specific type should be assignable to an array of a less specific type.
  • Having the latter not be the case would not be an acceptable type system in the vast majority of cases, so we have to take a correctness trade-off for the specific case of function argument types.
  • For example: – – Let’s look at the original function: – – Because ‘s type does not have an index signature, the compiler throws an error.

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Microsoft/TypeScript

Why developers like TaskBotJS

  • TaskBotJS is a job queue and processing service for NodeJS applications.
  • Using Redis as a background store, TaskBotJS allows you to offload long-running jobs away from your web application and handles all the rough edges involved: job scheduling, handling failures and retries, priority queueing, and the works

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Why developers like TaskBotJS

emotion

  • These definitions also infer types for css properties with the object syntax, HTML/SVG tag names, and prop types.
  • Typescript checks css properties with the object style syntax using csstype package, so following code will emit errors.
  • You can type the props of styled components.
  • By default, has an type annotation and works without any errors.
  • The types are the same as the types except that the types use Preact component types like and instead of React component types.

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emotion

webpack/webpack

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webpack/webpack

vuetifyjs/vuetify

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vuetifyjs/vuetify

Provide a better experience editing a file with merge-markers in it. by CyrusNajmabadi · Pull Request #15850 · dotnet/roslyn

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Provide a better experience editing a file with merge-markers in it. by CyrusNajmabadi · Pull Request #15850 · dotnet/roslyn

Release v0.10.1-beta · nemtech/nem2-sdk-typescript-javascript · GitHub

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Release v0.10.1-beta · nemtech/nem2-sdk-typescript-javascript · GitHub

TypeScript 2.9.1 変更点 – Qiita

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TypeScript 2.9.1 変更点 – Qiita

TypeScript 3.0.0-RC 変更点 – Qiita

  • // index.ts:18:17 – error TS2345: Argument of type ‘(word?
  • : string) => string’ is not assignable to parameter of type ‘(args_0: boolean) => string’.
  • // Types of parameters ‘word’ and ‘args_0’ are incompatible.
  • // Type ‘boolean’ is not assignable to type ‘string | undefined’.

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TypeScript 3.0.0-RC 変更点 – Qiita

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