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About

LogoHandbook - The TypeScript Handbooktypescriptlangchevron-right

Is a superset of Javascript empowering it by:

  • Static typing

  • Decorators

  • Generic types

  • Tuples

  • Modules

  • Better OO support with abstract classes

  • Interfaces

  • Visibility modifiers

  • And more...

Needs to be transpiled to Javascript.

  • Compiler: Transforms code to low code (machine-code).

  • Transpiler: Transforms code to other high level languages (source-to-source).

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Interoperability

Run js and ts in the same environment.

You can allow js to apply Typescript by creating a .d.ts file for a js file.

This file will have definitions typings for the js.

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Exploring the tsconfig.json

Centralizes all the code static analysis and transpilation rules.

Options

  • incremental: For incremental transpilation, saving cache that will speedup future transpilations, specially for big projects. Essentialy just transpile the changed files.

  • target: Defines the version of Javascript that will be utilized as the transpilation target.

    • es5 | ECMA2009: Older version from 2009.

    • es6 | ECMA2015: Which targets the ECMA from 2015.

    • ECMA2016: Is the default one. (Higher compatibility)

      • Adds ** exponential, ...

    • ECMA2017:

      • Adds async, ...

    • ECMA2018:

      • Adds rest \ spread, ...

    • ECMA2019:

    • ECMA2020:

      • Adds ??

    • ...

    • Check https://node.green/ for details of ECMA versions support in Node.js

      • Node 16.x and greater versions, do support up to ECMA2023.

      • ESNext is the versions with Stage 3, Stage 2 and Stage 1 releases

  • module: Important to define the type of module system to be used. - CommonJS - ES Modules

  • include: Defines which are the directories that must be included in the transpilation.

  • exclude: Defines which directores must be excluded in transpilation.

  • outFile: Used for projects that run in the browser, defining a file that will concatenate all the transpiled files.

  • outDir: Defines the directory that the transpiled files will be placed after transpilation.

  • allowJS: To allow js files to part of the typescript environment.

  • strict: Turn on several type checkings like:

    • strictNullChecks: Allow or not to accept if things return null | undefined and what will receive them cannot handle it.

    • strictFunctionTypes: Allow or not to scrictly compare functions types to the detail when assigning functions to variables.

    • strictBindCallApply: Allow of not to pass to fn.call(), parameters to the function that are not of the same type.

    • strictPropertyInitialization: Allow or not to have class properties to be declared but not initialized.

    • noImplicitAny: Allow or not using variables without typing, that can be automatically impliced typed.

    • noImplicitThis: Allow or not, when you have this cases, where the this is not pointing to where you think it is.

    • useUnknowInCatchVariables: Allow or not to use unknown error types in catch.

    • alwaysStrict: Will always put use strict in the transpiled file.

      • Not used anymore in recent versions of ECMA.

    • allowUnreachableCode: Allow or not leaving code that is unreachable.

    • noUnusedLocals: Allow or not leaving unused declared variables.

    • noUncheckedIndexedAccess: Allow or not to access dynamic properties of objects with ..

      • For Ex.: [prop: string]: string.

      • The right way to access woulb be with [].

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