TypeScript - KeynesYouDigIt/Knowledge GitHub Wiki

• Every project should have a tsconfig.json that says where the src files are, where the build files should go, what browsers should be targeted, etc.
• tslint is deprecated in favor of eslint
• Prefer local ts installations
  • `npm i -D typescript @types/node

• Built-ins - number, boolean, undefined, string, object (non-primative)
  • null and undefined are legal values for any other type (disablable)
• New types:
  • :any - Disables type checking
  • void
  • Arrays: can be done as number[] or Array<number>
  • Tuples: let x = [string, number, string]
  • Enum: enum Color {Red, Green, Blue}
    • Keeps numeric values
    • let color: Color = Color.Green; // 1
  • never: Errors, things that should never be called
  • ReadonlyArray<TypeGoesHere>: No mutation methods

Don't need to declare the object has having implemented the interface.

interface Person {
    name: string;
    optional?: boolean; // Optional property
    readonly dontWriteMe: string; // Like const for properties
    [propName: string]: any; // Any other properties
}

function announcePerson(person: Person) {
}

interface SendMessage {
    (recipient: Person, message: string): void
}
let messageFunction: SendMessage

messageFunction = function(recipient: Person, message: string): void {
    //
};

Comes after

const { old: new } : { old: number} = { old: 1 }

Make a type (like any) more specific.

let aString: any = "hey";
let aStringLength = (aString as string)

or

let aString: any = "hey";
let aStringLength = (<string>aString).length;

tsc

• --strictNullChecks - Saves a lot of headaches

• When importing modules, use npm i -D @types/package-name to use prebuilt type definitions
  • If it doesn't exist, put the following in a file to declare it as any:

// package-name.d.ts
declare module "package-name";