Sure. A function’s type consists of the types of its argument and its return type. Here we specify that the callback parameter’s type must be “function that accepts a number and returns type any“: class Foo { save(callback: (n: number) => any) : void { callback(42); } } var foo = new Foo(); var strCallback … Read more
TypeScript uses getter/setter syntax that is like ECMAScript4/ActionScript3. class foo { private _bar: boolean = false; get bar(): boolean { return this._bar; } set bar(value: boolean) { this._bar = value; } } That will produce this JavaScript, using the ECMAScript 5 Object.defineProperty() feature. var foo = (function () { function foo() { this._bar = false; … Read more
I just found the answer to this in another Stack Overflow question’s answer. declare global { interface Window { MyNamespace: any; } } window.MyNamespace = window.MyNamespace || {}; Basically, you need to extend the existing window interface to tell it about your new property.
That’s the non-null assertion operator. It is a way to tell the compiler “this expression cannot be null or undefined here, so don’t complain about the possibility of it being null or undefined.” Sometimes the type checker is unable to make that determination itself. It is explained here: A new ! post-fix expression operator may … Read more
RC6/RC7/Final release FIX To fix this error, you just need to import ReactiveFormsModule from @angular/forms in your module. Here’s the example of a basic module with ReactiveFormsModule import: import { NgModule } from ‘@angular/core’; import { BrowserModule } from ‘@angular/platform-browser’; import { FormsModule, ReactiveFormsModule } from ‘@angular/forms’; import { AppComponent } from ‘./app.component’; @NgModule({ imports: … Read more
Exactly like in JavaScript, you can use the parseInt or parseFloat functions, or simply use the unary + operator: var x = “32”; var y: number = +x; All of the mentioned techniques will have correct typing and will correctly parse simple decimal integer strings like “123”, but will behave differently for various other, possibly … Read more
The Constructor is a default method of the class that is executed when the class is instantiated and ensures proper initialisation of fields in the class and its subclasses. Angular, or better Dependency Injector (DI), analyses the constructor parameters and when it creates a new instance by calling new MyClass() it tries to find providers … Read more
I originally wrote this answer when TypeScript was still hot-off-the-presses. Five years later, this is an OK overview, but look at Lodewijk’s answer below for more depth 1000ft view… TypeScript is a superset of JavaScript which primarily provides optional static typing, classes and interfaces. One of the big benefits is to enable IDEs to provide … Read more
Yes, that’s it. In the app.module.ts file, I just added: import { FormsModule } from ‘@angular/forms’; […] @NgModule({ imports: [ […] FormsModule ], […] })
2019 Update The current answers and the official documentation are outdated. And for those new to TypeScript, the terminology used isn’t clear without examples. Below is a list of up-to-date differences. 1. Objects / Functions Both can be used to describe the shape of an object or a function signature. But the syntax differs. Interface … Read more