gulp

Symbol.iterator A method that returns the default iterator for an object. Called by the semantics of the for-of statement.

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.

Import a single export from a module import { ZipCodeValidator } from "./ZipCodeValidator"; let myValidator = new ZipCodeValidator(); imports can also be renamed import { ZipCodeValidator as ZCV } from "./ZipCodeValidator"; let myValidator = new ZCV();

Use Union Types Don’t write overloads that differ by type in only one argument position: /* WRONG */ interface Moment { utcOffset(): number; utcOffset(b: number): Moment; utcOffset(b: string): Moment; } Do use union types whenver possible: /* OK */ interface Moment { utcOffset(): number; utcOffset(b: number|string): Moment; } Note that we didn’t make b optional here because the return types of the signatures differ. Why: This is important for people who are “passing through” a value

Global-modifying Modules A global-modifying module alters existing values in the global scope when they are imported. For example, there might exist a library which adds new members to String.prototype when imported. This pattern is somewhat dangerous due to the possibility of runtime conflicts, but we can still write a declaration file for it.

Add TypeScript code Right click on scripts and click New Item. Then choose TypeScript File (it may be in the .NET Core section) and name the file app.ts.

Red flags

TypeScriptCompileBlocked If you are using a different build tool to build your project (e.g. gulp, grunt , etc.) and VS for the development and debugging experience, set <TypeScriptCompileBlocked>true</TypeScriptCompileBlocked> in your project. This should give you all the editing support, but not the build when you hit F5.

Optional Properties Not all properties of an interface may be required. Some exist under certain conditions or may not be there at all. These optional properties are popular when creating patterns like “option bags” where you pass an object to a function that only has a couple of properties filled in. Here’s an example of this pattern: interface SquareConfig { color?: string; width?: number; } function createSquare(config: SquareConfig): {color: string; area: number} { let newSquare = {c