book

Learning TypeScript

by Josh Goldberg

June 2022

Beginner

320 pages

6h 40m

English

O'Reilly Media, Inc.

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Who Should Read This BookWhy I Wrote This BookNavigating This BookExamples and ProjectsConventions Used in This BookUsing Code ExamplesO’Reilly Online LearningHow to Contact UsAcknowledgments
History of JavaScriptVanilla JavaScript’s PitfallsCostly FreedomLoose DocumentationWeaker Developer ToolingTypeScript!Getting Started in the TypeScript PlaygroundTypeScript in ActionFreedom Through RestrictionPrecise DocumentationStronger Developer ToolingCompiling SyntaxGetting Started LocallyRunning LocallyEditor FeaturesWhat TypeScript Is NotA Remedy for Bad CodeExtensions to JavaScript (Mostly)Slower Than JavaScriptFinished EvolvingSummary
What’s in a Type?Type SystemsKinds of ErrorsAssignabilityUnderstanding Assignability ErrorsType AnnotationsUnnecessary Type AnnotationsType ShapesModulesSummary
Union TypesDeclaring Union TypesUnion PropertiesNarrowingAssignment NarrowingConditional ChecksTypeof ChecksLiteral TypesLiteral AssignabilityStrict Null CheckingThe Billion-Dollar MistakeTruthiness NarrowingVariables Without Initial ValuesType AliasesType Aliases Are Not JavaScriptCombining Type AliasesSummary
Object TypesDeclaring Object TypesAliased Object TypesStructural TypingUsage CheckingExcess Property CheckingNested Object TypesOptional PropertiesUnions of Object TypesInferred Object-Type UnionsExplicit Object-Type UnionsNarrowing Object TypesDiscriminated UnionsIntersection TypesDangers of Intersection TypesSummary
Function ParametersRequired ParametersOptional ParametersDefault ParametersRest ParametersReturn TypesExplicit Return TypesFunction TypesFunction Type ParenthesesParameter Type InferencesFunction Type AliasesMore Return TypesVoid ReturnsNever ReturnsFunction OverloadsCall-Signature CompatibilitySummary
Array TypesArray and Function TypesUnion-Type ArraysEvolving Any ArraysMultidimensional ArraysArray MembersCaveat: Unsound MembersSpreads and RestsSpreadsSpreading Rest ParametersTuplesTuple AssignabilityTuple InferencesSummary
Type Aliases Versus InterfacesTypes of PropertiesOptional PropertiesRead-Only PropertiesFunctions and MethodsCall SignaturesIndex SignaturesNested InterfacesInterface ExtensionsOverridden PropertiesExtending Multiple InterfacesInterface MergingMember Naming ConflictsSummary

Class MethodsClass PropertiesFunction PropertiesInitialization CheckingOptional PropertiesRead-Only PropertiesClasses as TypesClasses and InterfacesImplementing Multiple InterfacesExtending a ClassExtension AssignabilityOverridden ConstructorsOverridden MethodsOverridden PropertiesAbstract ClassesMember VisibilityStatic Field ModifiersSummary
Top Typesany, AgainunknownType PredicatesType OperatorskeyoftypeofType AssertionsAsserting Caught Error TypesNon-Null AssertionsType Assertion CaveatsConst AssertionsLiterals to PrimitivesRead-Only ObjectsSummary
Generic FunctionsExplicit Generic Call TypesMultiple Function Type ParametersGeneric InterfacesInferred Generic Interface TypesGeneric ClassesExplicit Generic Class TypesExtending Generic ClassesImplementing Generic InterfacesMethod GenericsStatic Class GenericsGeneric Type AliasesGeneric Discriminated UnionsGeneric ModifiersGeneric DefaultsConstrained Generic Typeskeyof and Constrained Type ParametersPromisesCreating PromisesAsync FunctionsUsing Generics RightThe Golden Rule of GenericsGeneric Naming ConventionsSummary
Declaration FilesDeclaring Runtime ValuesGlobal ValuesGlobal Interface MergingGlobal AugmentationsBuilt-In DeclarationsLibrary DeclarationsDOM DeclarationsModule DeclarationsWildcard Module DeclarationsPackage TypesdeclarationDependency Package TypesExposing Package TypesDefinitelyTypedType AvailabilitySummary
Navigating CodeFinding DefinitionsFinding ReferencesFinding ImplementationsWriting CodeCompleting NamesAutomatic Import UpdatesCode ActionsWorking Effectively with ErrorsLanguage Service ErrorsSummary
tsc OptionsPretty ModeWatch ModeTSConfig Filestsc --initCLI Versus ConfigurationFile InclusionsincludeexcludeAlternative ExtensionsJSX SyntaxresolveJsonModuleEmitoutDirtargetEmitting DeclarationsSource MapsnoEmitType CheckinglibskipLibCheckStrict ModeModulesmodulemoduleResolutionInteroperability with CommonJSisolatedModulesJavaScriptallowJscheckJsJSDoc SupportConfiguration ExtensionsextendsConfiguration BasesProject ReferencescompositereferencesBuild ModeSummary
Class Parameter PropertiesExperimental DecoratorsEnumsAutomatic Numeric ValuesString-Valued EnumsConst EnumsNamespacesNamespace ExportsNested NamespacesNamespaces in Type DefinitionsPrefer Modules Over NamespacesType-Only Imports and ExportsSummary
Mapped TypesMapped Types from TypesChanging ModifiersGeneric Mapped TypesConditional TypesGeneric Conditional TypesType DistributivityInferred TypesMapped Conditional Typesnevernever and Intersections and Unionsnever and Conditional Typesnever and Mapped TypesTemplate Literal TypesIntrinsic String Manipulation TypesTemplate Literal KeysRemapping Mapped Type KeysType Operations and ComplexitySummary

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About the Author

Josh Goldberg is a frontend developer from New York with a passion for open source, static analysis, and the web. He is a full-time open source maintainer who contributes regularly to TypeScript and open source projects in its ecosystem, such as typescript-eslint and TypeStat. His past work includes spearheading Codecademy’s usage of TypeScript, helping create its Learn TypeScript course, and architecting rich client applications at Microsoft. His projects range from static analysis to meta-languages to re-creating retro games in the browser. Also cats.