Early Benefits Even at this point you can get some great benefits from TypeScript understanding your project. If you open up an editor like VS Code or Visual Studio, you’ll see that you can often get some tooling support like completion. You can also catch certain bugs with options like: noImplicitReturns which prevents you from forgetting to return at the end of a function. noFallthroughCasesInSwitch which is helpful if you never want to forget a break statement between cases in a switch blo

Enums Enums are compatible with numbers, and numbers are compatible with enums. Enum values from different enum types are considered incompatible. For example, enum Status { Ready, Waiting }; enum Color { Red, Blue, Green }; let status = Status.Ready; status = Color.Green; //error

Download packages from NPM Install PackageInstaller. Use PackageInstaller to install Angular 2, systemjs and Typings. Right-click on the project, then click on Quick Install Package. Use PackageInstaller to install typings for es6-shim. Angular 2 includes es6-shim for Promise support, but TypeScript still needs the types. In PackageInstaller, choose Typing instead of npm. Then type “es6-shim”:

Details The "compilerOptions" property can be omitted, in which case the compiler’s defaults are used. See our full list of supported Compiler Options. The "files" property takes a list of relative or absolute file paths. The "include" and "exclude" properties take a list of glob-like file patterns. The supported glob wildcards are: * matches zero or more characters (excluding directory separators) ? matches any one character (excluding directory separators) **/ recursively matches any subdi

Discriminated Unions You can combine string literal types, union types, type guards, and type aliases to build an advanced pattern called discriminated unions, also known as tagged unions or algebraic data types. Discriminated unions are useful in functional programming. Some languages automatically discriminate unions for you; TypeScript instead builds on JavaScript patterns as they exist today. There are four ingredients: Types that have a common, string literal property — the discriminant. A

Disallowed Merges Not all merges are allowed in TypeScript. Currently, classes can not merge with other classes or with variables. For information on mimicking class merging, see the Mixins in TypeScript section.

Downloading Getting type declarations in TypeScript 2.0 and above requires no tools apart from npm. As an example, getting the declarations for a library like lodash takes nothing more than the following command npm install --save @types/lodash

Destructuring Another ECMAScript 2015 feature that TypeScript has is destructuring. For a complete reference, see the article on the Mozilla Developer Network. In this section, we’ll give a short overview.

Dependencies on Global Libraries If your library depends on a global library, use a /// <reference types="..." /> directive: /// <reference types="someLib" /> function getThing(): someLib.thing;

Definition File Theory: A Deep Dive Structuring modules to give the exact API shape you want can be tricky. For example, we might want a module that can be invoked with or without new to produce different types, has a variety of named types exposed in a hierarchy, and has some properties on the module object as well. By reading this guide, you’ll have the tools to write complex definition files that expose a friendly API surface. This guide focuses on module (or UMD) libraries because the optio