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Title: TypeScript: Documentation - TypeScript 3.7

Open Graph Title: Documentation - TypeScript 3.7

Description: TypeScript 3.7 Release Notes

Open Graph Description: TypeScript 3.7 Release Notes

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Skip to main contenthttps://www.typescriptlang.org/docs/handbook/release-notes/typescript-3-7.html#handbook-content
TypeScripthttps://www.typescriptlang.org/
Downloadhttps://www.typescriptlang.org/download/
Docshttps://www.typescriptlang.org/docs/
Handbookhttps://www.typescriptlang.org/docs/handbook/intro.html
Communityhttps://www.typescriptlang.org/community/
Playgroundhttps://www.typescriptlang.org/play/
Toolshttps://www.typescriptlang.org/tools/
in Enhttps://www.typescriptlang.org/docs/handbook/release-notes/typescript-3-7.html
TS for the New Programmerhttps://www.typescriptlang.org/docs/handbook/typescript-from-scratch.html
TypeScript for JS Programmershttps://www.typescriptlang.org/docs/handbook/typescript-in-5-minutes.html
TS for Java/C# Programmershttps://www.typescriptlang.org/docs/handbook/typescript-in-5-minutes-oop.html
TS for Functional Programmershttps://www.typescriptlang.org/docs/handbook/typescript-in-5-minutes-func.html
TypeScript Tooling in 5 minuteshttps://www.typescriptlang.org/docs/handbook/typescript-tooling-in-5-minutes.html
The TypeScript Handbookhttps://www.typescriptlang.org/docs/handbook/intro.html
The Basicshttps://www.typescriptlang.org/docs/handbook/2/basic-types.html
Everyday Typeshttps://www.typescriptlang.org/docs/handbook/2/everyday-types.html
Narrowinghttps://www.typescriptlang.org/docs/handbook/2/narrowing.html
More on Functionshttps://www.typescriptlang.org/docs/handbook/2/functions.html
Object Typeshttps://www.typescriptlang.org/docs/handbook/2/objects.html
Creating Types from Typeshttps://www.typescriptlang.org/docs/handbook/2/types-from-types.html
Genericshttps://www.typescriptlang.org/docs/handbook/2/generics.html
Keyof Type Operatorhttps://www.typescriptlang.org/docs/handbook/2/keyof-types.html
Typeof Type Operatorhttps://www.typescriptlang.org/docs/handbook/2/typeof-types.html
Indexed Access Typeshttps://www.typescriptlang.org/docs/handbook/2/indexed-access-types.html
Conditional Typeshttps://www.typescriptlang.org/docs/handbook/2/conditional-types.html
Mapped Typeshttps://www.typescriptlang.org/docs/handbook/2/mapped-types.html
Template Literal Typeshttps://www.typescriptlang.org/docs/handbook/2/template-literal-types.html
Classeshttps://www.typescriptlang.org/docs/handbook/2/classes.html
Moduleshttps://www.typescriptlang.org/docs/handbook/2/modules.html
Utility Typeshttps://www.typescriptlang.org/docs/handbook/utility-types.html
Cheat Sheetshttps://www.typescriptlang.org/cheatsheets/
Decoratorshttps://www.typescriptlang.org/docs/handbook/decorators.html
Declaration Merginghttps://www.typescriptlang.org/docs/handbook/declaration-merging.html
Enumshttps://www.typescriptlang.org/docs/handbook/enums.html
Iterators and Generatorshttps://www.typescriptlang.org/docs/handbook/iterators-and-generators.html
JSXhttps://www.typescriptlang.org/docs/handbook/jsx.html
Mixinshttps://www.typescriptlang.org/docs/handbook/mixins.html
Namespaceshttps://www.typescriptlang.org/docs/handbook/namespaces.html
Namespaces and Moduleshttps://www.typescriptlang.org/docs/handbook/namespaces-and-modules.html
Symbolshttps://www.typescriptlang.org/docs/handbook/symbols.html
Triple-Slash Directiveshttps://www.typescriptlang.org/docs/handbook/triple-slash-directives.html
Type Compatibilityhttps://www.typescriptlang.org/docs/handbook/type-compatibility.html
Type Inferencehttps://www.typescriptlang.org/docs/handbook/type-inference.html
Variable Declarationhttps://www.typescriptlang.org/docs/handbook/variable-declarations.html
Introductionhttps://www.typescriptlang.org/docs/handbook/modules/introduction.html
Theoryhttps://www.typescriptlang.org/docs/handbook/modules/theory.html
Choosing Compiler Optionshttps://www.typescriptlang.org/docs/handbook/modules/guides/choosing-compiler-options.html
Referencehttps://www.typescriptlang.org/docs/handbook/modules/reference.html
ESM/CJS Interoperabilityhttps://www.typescriptlang.org/docs/handbook/modules/appendices/esm-cjs-interop.html
ASP.NET Corehttps://www.typescriptlang.org/docs/handbook/asp-net-core.html
Gulphttps://www.typescriptlang.org/docs/handbook/gulp.html
DOM Manipulationhttps://www.typescriptlang.org/docs/handbook/dom-manipulation.html
Migrating from JavaScripthttps://www.typescriptlang.org/docs/handbook/migrating-from-javascript.html
Using Babel with TypeScripthttps://www.typescriptlang.org/docs/handbook/babel-with-typescript.html
TypeScript 6.0https://www.typescriptlang.org/docs/handbook/release-notes/typescript-6-0.html
TypeScript 5.9https://www.typescriptlang.org/docs/handbook/release-notes/typescript-5-9.html
TypeScript 5.8https://www.typescriptlang.org/docs/handbook/release-notes/typescript-5-8.html
TypeScript 5.7https://www.typescriptlang.org/docs/handbook/release-notes/typescript-5-7.html
TypeScript 5.6https://www.typescriptlang.org/docs/handbook/release-notes/typescript-5-6.html
TypeScript 5.5https://www.typescriptlang.org/docs/handbook/release-notes/typescript-5-5.html
TypeScript 5.4https://www.typescriptlang.org/docs/handbook/release-notes/typescript-5-4.html
TypeScript 5.3https://www.typescriptlang.org/docs/handbook/release-notes/typescript-5-3.html
TypeScript 5.2https://www.typescriptlang.org/docs/handbook/release-notes/typescript-5-2.html
TypeScript 5.1https://www.typescriptlang.org/docs/handbook/release-notes/typescript-5-1.html
TypeScript 5.0https://www.typescriptlang.org/docs/handbook/release-notes/typescript-5-0.html
TypeScript 4.9https://www.typescriptlang.org/docs/handbook/release-notes/typescript-4-9.html
TypeScript 4.8https://www.typescriptlang.org/docs/handbook/release-notes/typescript-4-8.html
TypeScript 4.7https://www.typescriptlang.org/docs/handbook/release-notes/typescript-4-7.html
TypeScript 4.6https://www.typescriptlang.org/docs/handbook/release-notes/typescript-4-6.html
TypeScript 4.5https://www.typescriptlang.org/docs/handbook/release-notes/typescript-4-5.html
TypeScript 4.4https://www.typescriptlang.org/docs/handbook/release-notes/typescript-4-4.html
TypeScript 4.3https://www.typescriptlang.org/docs/handbook/release-notes/typescript-4-3.html
TypeScript 4.2https://www.typescriptlang.org/docs/handbook/release-notes/typescript-4-2.html
TypeScript 4.1https://www.typescriptlang.org/docs/handbook/release-notes/typescript-4-1.html
TypeScript 4.0https://www.typescriptlang.org/docs/handbook/release-notes/typescript-4-0.html
TypeScript 3.9https://www.typescriptlang.org/docs/handbook/release-notes/typescript-3-9.html
TypeScript 3.8https://www.typescriptlang.org/docs/handbook/release-notes/typescript-3-8.html
TypeScript 3.7https://www.typescriptlang.org/docs/handbook/release-notes/typescript-3-7.html
TypeScript 3.6https://www.typescriptlang.org/docs/handbook/release-notes/typescript-3-6.html
TypeScript 3.5https://www.typescriptlang.org/docs/handbook/release-notes/typescript-3-5.html
TypeScript 3.4https://www.typescriptlang.org/docs/handbook/release-notes/typescript-3-4.html
TypeScript 3.3https://www.typescriptlang.org/docs/handbook/release-notes/typescript-3-3.html
TypeScript 3.2https://www.typescriptlang.org/docs/handbook/release-notes/typescript-3-2.html
TypeScript 3.1https://www.typescriptlang.org/docs/handbook/release-notes/typescript-3-1.html
TypeScript 3.0https://www.typescriptlang.org/docs/handbook/release-notes/typescript-3-0.html
TypeScript 2.9https://www.typescriptlang.org/docs/handbook/release-notes/typescript-2-9.html
TypeScript 2.8https://www.typescriptlang.org/docs/handbook/release-notes/typescript-2-8.html
TypeScript 2.7https://www.typescriptlang.org/docs/handbook/release-notes/typescript-2-7.html
TypeScript 2.6https://www.typescriptlang.org/docs/handbook/release-notes/typescript-2-6.html
TypeScript 2.5https://www.typescriptlang.org/docs/handbook/release-notes/typescript-2-5.html
TypeScript 2.4https://www.typescriptlang.org/docs/handbook/release-notes/typescript-2-4.html
TypeScript 2.3https://www.typescriptlang.org/docs/handbook/release-notes/typescript-2-3.html
TypeScript 2.2https://www.typescriptlang.org/docs/handbook/release-notes/typescript-2-2.html
TypeScript 2.1https://www.typescriptlang.org/docs/handbook/release-notes/typescript-2-1.html
TypeScript 2.0https://www.typescriptlang.org/docs/handbook/release-notes/typescript-2-0.html
TypeScript 1.8https://www.typescriptlang.org/docs/handbook/release-notes/typescript-1-8.html
TypeScript 1.7https://www.typescriptlang.org/docs/handbook/release-notes/typescript-1-7.html
TypeScript 1.6https://www.typescriptlang.org/docs/handbook/release-notes/typescript-1-6.html
TypeScript 1.5https://www.typescriptlang.org/docs/handbook/release-notes/typescript-1-5.html
TypeScript 1.4https://www.typescriptlang.org/docs/handbook/release-notes/typescript-1-4.html
TypeScript 1.3https://www.typescriptlang.org/docs/handbook/release-notes/typescript-1-3.html
TypeScript 1.1https://www.typescriptlang.org/docs/handbook/release-notes/typescript-1-1.html
Introductionhttps://www.typescriptlang.org/docs/handbook/declaration-files/introduction.html
Declaration Referencehttps://www.typescriptlang.org/docs/handbook/declaration-files/by-example.html
Library Structureshttps://www.typescriptlang.org/docs/handbook/declaration-files/library-structures.html
Modules .d.tshttps://www.typescriptlang.org/docs/handbook/declaration-files/templates/module-d-ts.html
Module: Pluginhttps://www.typescriptlang.org/docs/handbook/declaration-files/templates/module-plugin-d-ts.html
Module: Classhttps://www.typescriptlang.org/docs/handbook/declaration-files/templates/module-class-d-ts.html
Module: Functionhttps://www.typescriptlang.org/docs/handbook/declaration-files/templates/module-function-d-ts.html
Global .d.tshttps://www.typescriptlang.org/docs/handbook/declaration-files/templates/global-d-ts.html
Global: Modifying Modulehttps://www.typescriptlang.org/docs/handbook/declaration-files/templates/global-modifying-module-d-ts.html
Do's and Don'tshttps://www.typescriptlang.org/docs/handbook/declaration-files/do-s-and-don-ts.html
Deep Divehttps://www.typescriptlang.org/docs/handbook/declaration-files/deep-dive.html
Publishinghttps://www.typescriptlang.org/docs/handbook/declaration-files/publishing.html
Consumptionhttps://www.typescriptlang.org/docs/handbook/declaration-files/consumption.html
JS Projects Utilizing TypeScripthttps://www.typescriptlang.org/docs/handbook/intro-to-js-ts.html
Type Checking JavaScript Fileshttps://www.typescriptlang.org/docs/handbook/type-checking-javascript-files.html
JSDoc Referencehttps://www.typescriptlang.org/docs/handbook/jsdoc-supported-types.html
Creating .d.ts Files from .js fileshttps://www.typescriptlang.org/docs/handbook/declaration-files/dts-from-js.html
What is a tsconfig.jsonhttps://www.typescriptlang.org/docs/handbook/tsconfig-json.html
Compiler Options in MSBuildhttps://www.typescriptlang.org/docs/handbook/compiler-options-in-msbuild.html
TSConfig Referencehttps://www.typescriptlang.org/tsconfig/
tsc CLI Optionshttps://www.typescriptlang.org/docs/handbook/compiler-options.html
Project Referenceshttps://www.typescriptlang.org/docs/handbook/project-references.html
Integrating with Build Toolshttps://www.typescriptlang.org/docs/handbook/integrating-with-build-tools.html
Configuring Watchhttps://www.typescriptlang.org/docs/handbook/configuring-watch.html
Nightly Buildshttps://www.typescriptlang.org/docs/handbook/nightly-builds.html
https://www.typescriptlang.org/docs/handbook/release-notes/typescript-3-7.html#optional-chaining
Playgroundhttps://www.typescriptlang.org/play/#example/optional-chaining
issue #16https://github.com/microsoft/TypeScript/issues/16
strictNullCheckshttps://www.typescriptlang.org/tsconfig#strictNullChecks
read up on the proposalhttps://github.com/tc39/proposal-optional-chaining/
view the original pull requesthttps://github.com/microsoft/TypeScript/pull/33294
https://www.typescriptlang.org/docs/handbook/release-notes/typescript-3-7.html#nullish-coalescing
Playgroundhttps://www.typescriptlang.org/play/#example/nullish-coalescing
localStoragehttps://developer.mozilla.org/docs/Web/API/Window/localStorage
Wenlu Wanghttps://github.com/Kingwl
Titian Cernicova Dragomirhttps://github.com/dragomirtitian
check out their pull requesthttps://github.com/microsoft/TypeScript/pull/32883
the nullish coalescing proposal repositoryhttps://github.com/tc39/proposal-nullish-coalescing/
https://www.typescriptlang.org/docs/handbook/release-notes/typescript-3-7.html#assertion-functions
Playgroundhttps://www.typescriptlang.org/play/#example/assertion-functions
check out the original pull requesthttps://github.com/microsoft/TypeScript/pull/32695
https://www.typescriptlang.org/docs/handbook/release-notes/typescript-3-7.html#better-support-for-never-returning-functions
process.exit(...) in @types/nodehttps://github.com/DefinitelyTyped/DefinitelyTyped/blob/5299d372a220584e75a031c13b3d555607af13f8/types/node/globals.d.ts#l874
read up more at the same pull requesthttps://github.com/microsoft/TypeScript/pull/32695
https://www.typescriptlang.org/docs/handbook/release-notes/typescript-3-7.html#more-recursive-type-aliases
Playgroundhttps://www.typescriptlang.org/play/#example/recursive-type-references
consistent with how other languages treat type aliaseshttps://wikipedia.org/w/index.php?title=Recursive_data_type&oldid=913091335#in_type_synonyms
read up on the original pull requesthttps://github.com/microsoft/TypeScript/pull/33050
https://www.typescriptlang.org/docs/handbook/release-notes/typescript-3-7.html#--declaration-and---allowjs
declarationhttps://www.typescriptlang.org/tsconfig#declaration
declarationhttps://www.typescriptlang.org/tsconfig#declaration
allowJshttps://www.typescriptlang.org/tsconfig#allowJs
declarationhttps://www.typescriptlang.org/tsconfig#declaration
allowJshttps://www.typescriptlang.org/tsconfig#allowJs
declarationhttps://www.typescriptlang.org/tsconfig#declaration
emitDeclarationOnlyhttps://www.typescriptlang.org/tsconfig#emitDeclarationOnly
check out the original pull requesthttps://github.com/microsoft/TypeScript/pull/32372
https://www.typescriptlang.org/docs/handbook/release-notes/typescript-3-7.html#the-usedefineforclassfields-flag-and-the-declare-property-modifier
useDefineForClassFieldshttps://www.typescriptlang.org/tsconfig#useDefineForClassFields
useDefineForClassFieldshttps://www.typescriptlang.org/tsconfig#useDefineForClassFields
noEmithttps://www.typescriptlang.org/tsconfig#noEmit
take a look at the original pull request for these changeshttps://github.com/microsoft/TypeScript/pull/33509
useDefineForClassFieldshttps://www.typescriptlang.org/tsconfig#useDefineForClassFields
https://www.typescriptlang.org/docs/handbook/release-notes/typescript-3-7.html#build-free-editing-with-project-references
disableSourceOfProjectReferenceRedirecthttps://www.typescriptlang.org/tsconfig#disableSourceOfProjectReferenceRedirect
read up more about this change by reading up on its pull requesthttps://github.com/microsoft/TypeScript/pull/32028
https://www.typescriptlang.org/docs/handbook/release-notes/typescript-3-7.html#uncalled-function-checks
strictNullCheckshttps://www.typescriptlang.org/tsconfig#strictNullChecks
@jwbayhttps://github.com/jwbay
proof-of-concepthttps://github.com/microsoft/TypeScript/pull/32802
the current versionhttps://github.com/microsoft/TypeScript/pull/33178
https://www.typescriptlang.org/docs/handbook/release-notes/typescript-3-7.html#-ts-nocheck-in-typescript-files
checkJshttps://www.typescriptlang.org/tsconfig#checkJs
https://www.typescriptlang.org/docs/handbook/release-notes/typescript-3-7.html#semicolon-formatter-option
Visual Studio Code Insidershttps://code.visualstudio.com/insiders/
https://www.typescriptlang.org/docs/handbook/release-notes/typescript-3-7.html#37-breaking-changes
https://www.typescriptlang.org/docs/handbook/release-notes/typescript-3-7.html#dom-changes
Types in lib.dom.d.ts have been updatedhttps://github.com/microsoft/TypeScript/pull/33627
https://www.typescriptlang.org/docs/handbook/release-notes/typescript-3-7.html#class-field-mitigations
As mentioned abovehttps://www.typescriptlang.org/docs/handbook/release-notes/typescript-3-7.html#the-usedefineforclassfields-flag-and-the-declare-property-modifier
useDefineForClassFieldshttps://www.typescriptlang.org/tsconfig#useDefineForClassFields
the section above on the useDefineForClassFields flaghttps://www.typescriptlang.org/docs/handbook/release-notes/typescript-3-7.html#the-usedefineforclassfields-flag-and-the-declare-property-modifier
https://www.typescriptlang.org/docs/handbook/release-notes/typescript-3-7.html#function-truthy-checks
strictNullCheckshttps://www.typescriptlang.org/tsconfig#strictNullChecks
https://www.typescriptlang.org/docs/handbook/release-notes/typescript-3-7.html#local-and-imported-type-declarations-now-conflict
this is now correctly identified as a duplicate identifier errorhttps://github.com/microsoft/TypeScript/pull/31231
https://www.typescriptlang.org/docs/handbook/release-notes/typescript-3-7.html#37-api-changes
Optional Chaininghttps://www.typescriptlang.org/docs/handbook/release-notes/typescript-3-7.html#optional-chaining
Nullish Coalescinghttps://www.typescriptlang.org/docs/handbook/release-notes/typescript-3-7.html#nullish-coalescing
Assertion Functionshttps://www.typescriptlang.org/docs/handbook/release-notes/typescript-3-7.html#assertion-functions
Better Support for never-Returning Functionshttps://www.typescriptlang.org/docs/handbook/release-notes/typescript-3-7.html#better-support-for-never-returning-functions
(More) Recursive Type Aliaseshttps://www.typescriptlang.org/docs/handbook/release-notes/typescript-3-7.html#more-recursive-type-aliases
--declaration and --allowJshttps://www.typescriptlang.org/docs/handbook/release-notes/typescript-3-7.html#--declaration-and---allowjs
The useDefineForClassFields Flag and The declare Property Modifierhttps://www.typescriptlang.org/docs/handbook/release-notes/typescript-3-7.html#the-usedefineforclassfields-flag-and-the-declare-property-modifier
Build-Free Editing with Project Referenceshttps://www.typescriptlang.org/docs/handbook/release-notes/typescript-3-7.html#build-free-editing-with-project-references
Uncalled Function Checkshttps://www.typescriptlang.org/docs/handbook/release-notes/typescript-3-7.html#uncalled-function-checks
// @ts-nocheck in TypeScript Fileshttps://www.typescriptlang.org/docs/handbook/release-notes/typescript-3-7.html#-ts-nocheck-in-typescript-files
Semicolon Formatter Optionhttps://www.typescriptlang.org/docs/handbook/release-notes/typescript-3-7.html#semicolon-formatter-option
3.7 Breaking Changeshttps://www.typescriptlang.org/docs/handbook/release-notes/typescript-3-7.html#37-breaking-changes
DOM Changeshttps://www.typescriptlang.org/docs/handbook/release-notes/typescript-3-7.html#dom-changes
Class Field Mitigationshttps://www.typescriptlang.org/docs/handbook/release-notes/typescript-3-7.html#class-field-mitigations
Function Truthy Checkshttps://www.typescriptlang.org/docs/handbook/release-notes/typescript-3-7.html#function-truthy-checks
Local and Imported Type Declarations Now Conflicthttps://www.typescriptlang.org/docs/handbook/release-notes/typescript-3-7.html#local-and-imported-type-declarations-now-conflict
3.7 API Changeshttps://www.typescriptlang.org/docs/handbook/release-notes/typescript-3-7.html#37-api-changes
by sending a Pull Requesthttps://github.com/microsoft/TypeScript-Website/blob/v2/packages/documentation/copy/en/release-notes/TypeScript 3.7.md
Everyday Typeshttps://www.typescriptlang.org/docs/handbook/2/everyday-types.html
Creating Types from Typeshttps://www.typescriptlang.org/docs/handbook/2/types-from-types.html
More on Functionshttps://www.typescriptlang.org/docs/handbook/2/functions.html
More on Objectshttps://www.typescriptlang.org/docs/handbook/2/objects.html
Narrowinghttps://www.typescriptlang.org/docs/handbook/2/narrowing.html
Variable Declarationshttps://www.typescriptlang.org/docs/handbook/variable-declarations.html
TypeScript in 5 minuteshttps://www.typescriptlang.org/docs/handbook/typescript-in-5-minutes.html
TSConfig Optionshttps://www.typescriptlang.org/tsconfig/
Classeshttps://www.typescriptlang.org/docs/handbook/2/classes.html
https://www.typescriptlang.org/docs/handbook/release-notes/typescript-3-7.html
Privacyhttps://go.microsoft.com/fwlink/?LinkId=521839
Terms of Usehttps://go.microsoft.com/fwlink/?LinkID=206977
Get Startedhttps://www.typescriptlang.org/docs/
Downloadhttps://www.typescriptlang.org/download/
Communityhttps://www.typescriptlang.org/community/
Playgroundhttps://www.typescriptlang.org/play/
TSConfig Refhttps://www.typescriptlang.org/tsconfig/
Code Sampleshttps://www.typescriptlang.org/play/#show-examples
Why TypeScripthttps://www.typescriptlang.org/why-create-typescript/
Designhttps://www.typescriptlang.org/branding/
Get Helphttps://www.typescriptlang.org/community
Bloghttps://devblogs.microsoft.com/typescript/
GitHub Repohttps://github.com/microsoft/TypeScript/#readme
Community Chathttps://discord.gg/typescript
@TypeScripthttps://twitter.com/TypeScript
Mastodonhttps://fosstodon.org/@TypeScript
Stack Overflowhttps://stackoverflow.com/questions/tagged/typescript
Web Repohttps://github.com/microsoft/TypeScript-Website

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