Let's get started by building a simple web application with TypeScript.There are two main ways to get the TypeScript tools:

First, install ASP.NET Core if you need it. This quick-start guide requires Visual Studio 2015 or 2017.Next, if your version of Visual Studio does not already have the latest TypeScript, you can install it.

This quick start guide will teach you how to build TypeScript with gulp and then add Browserify, uglify, or Watchify to the gulp pipeline.This guide also shows how to add Babel functionality using Babelify.We assume that you're already using Node.js with npm.

TypeScript doesn't exist in a vacuum.It was built with the JavaScript ecosystem in mind, and a lot of JavaScript exists today.Converting a JavaScript codebase over to TypeScript is, while somewhat tedious, usually not challenging.

This guide will teach you how to wire up TypeScript with React and webpack.If you're starting a brand new project, take a look at the React Quick Start guide first.Otherwise, we assume that you're already using Node.js with npm.

For programs to be useful, we need to be able to work with some of the simplest units of data: numbers, strings, structures, boolean values, and the like.In TypeScript, we support much the same types as you would expect in JavaScript, with a convenient enumeration type thrown in to help things along.The most basic datatype is the simple true/false value, which JavaScript and TypeScript call a boolean value.

let and const are two relatively new types of variable declarations in JavaScript.As we mentioned earlier, let is similar to var in some respects, but allows users to avoid some of the common "gotchas" that users run into in JavaScript.const is an augmentation of let in that it prevents re-assignment to a variable.

One of TypeScript's core principles is that type checking focuses on the shape that values have.This is sometimes called "duck typing" or "structural subtyping".In TypeScript, interfaces fill the role of naming these types, and are a powerful way of defining contracts within your code as well as contracts with code outside of your project.

Traditional JavaScript uses functions and prototype-based inheritance to build up reusable components, but this may feel a bit awkward to programmers more comfortable with an object-oriented approach, where classes inherit functionality and objects are built from these classes.Starting with ECMAScript 2015, also known as ECMAScript 6, JavaScript programmers will be able to build their applications using this object-oriented class-based approach.In TypeScript, we allow developers to use these

Functions are the fundamental building block of any application in JavaScript.They're how you build up layers of abstraction, mimicking classes, information hiding, and modules.In TypeScript, while there are classes, namespaces, and modules, functions still play the key role in describing how to do things.

A major part of software engineering is building components that not only have well-defined and consistent APIs, but are also reusable.Components that are capable of working on the data of today as well as the data of tomorrow will give you the most flexible capabilities for building up large software systems.In languages like C# and Java, one of the main tools in the toolbox for creating reusable components is generics, that is, being able to create a component that can work over a variet

Enums allow us to define a set of named constants.Using enums can make it easier to document intent, or create a set of distinct cases.TypeScript provides both numeric and string-based enums.

In this section, we will cover type inference in TypeScript. Namely, we'll discuss where and how types are inferred.In TypeScript, there are several places where type inference is used to provide type information when there is no explicit type annotation. For example, in this codelet x = 3;

Type compatibility in TypeScript is based on structural subtyping.Structural typing is a way of relating types based solely on their members.This is in contrast with nominal typing.

An intersection type combines multiple types into one.This allows you to add together existing types to get a single type that has all the features you need.For example, Person & Serializable & Loggable is a Person and Serializable and Loggable.

Starting with ECMAScript 2015, symbol is a primitive data type, just like number and string.symbol values are created by calling the Symbol constructor.let sym1 = Symbol();

An object is deemed iterable if it has an implementation for the Symbol.iterator">Symbol.iterator property.Some built-in types like Array, Map, Set, String, Int32Array, Uint32Array, etc. have their Symbol.iterator property already implemented.Symbol.iterator function on an object is responsible for returning the list of values to iterate on.

A note about terminology:It's important to note that in TypeScript 1.5, the nomenclature has changed."Internal modules" are now "namespaces".

IntroductionFirst steps

A note about terminology:It's important to note that in TypeScript 1.5, the nomenclature has changed."Internal modules" are now "namespaces".

This section assumes some basic knowledge about modules.Please see the Modules documentation for more information.Module resolution is the process the compiler uses to figure out what an import refers to.

Some of the unique concepts in TypeScript describe the shape of JavaScript objects at the type level.One example that is especially unique to TypeScript is the concept of 'declaration merging'.Understanding this concept will give you an advantage when working with existing JavaScript.

IntroductionBasic UsageThe as operator

With the introduction of Classes in TypeScript and ES6, there now exist certain scenarios that require additional features to support annotating or modifying classes and class members.Decorators provide a way to add both annotations and a meta-programming syntax for class declarations and members.Decorators are a stage 2 proposal for JavaScript and are available as an experimental feature of TypeScript.

IntroductionMixin sampleUnderstanding the sample

Triple-slash directives are single-line comments containing a single XML tag.The contents of the comment are used as compiler directives.Triple-slash directives are only valid at the top of their containing file.

TypeScript 2.3 and later support type-checking and reporting errors in .js files with --checkJs.You can skip checking some files by adding a // @ts-nocheck comment to them; conversely, you can choose to check only a few .js files by adding a // @ts-check comment to them without setting --checkJs.You can also ignore errors on specific lines by adding // @ts-ignore on the preceding line.

Option | Type | Default | Description--allowJs | boolean | false | Allow JavaScript files to be compiled.--allowSyntheticDefaultImports | boolean | module === "system" or --esModuleInterop | Allow default imports from modules with no default export. This does not affect code emit, just typechecking.

Project references are a new feature in TypeScript 3.0 that allow you to structure your TypeScript programs into smaller pieces.By doing this, you can greatly improve build times, enforce logical separation between components, and organize your code in new and better ways.We're also introducing a new mode for tsc, the --build flag, that works hand in hand with project references to enable faster TypeScript builds.

Compiler options can be specified using MSBuild properties within an MSBuild project.<PropertyGroup Condition="'$(Configuration)' == 'Debug'"> <TypeScriptRemoveComments>false</TypeScriptRemoveComments>

Build tools

A nightly build from the master">TypeScript's master branch is published by midnight PST to NPM and NuGet.Here is how you can get it and use it with your tools.npm install -g typescript@next