typescript.md

TypeScript

Why TypeScript

There are two main goals of TypeScript:

• Provide an optional type system for JavaScript.
• Provide planned features from future JavaScript editions to current JavaScript engines

sample.js (JavaScript)

let foo = 123;

sample.ts (TypeScript)

let foo: number = 123

Types increase your agility when doing refactoring. Its better for the compiler to catch errors than to have things fail at runtime.

Types are structural

interface Point2D {
    x: number;
    y: number;
}
interface Point3D {
    x: number;
    y: number;
    z: number;
}

var point2D: Point2D = { x: 0, y: 10, }
var point3D: Point3D = { x: 0, y: 10, z: 20 }
function iTakePoint2D(point: Point2D) { /* do something */ }

iTakePoint2D(point2D); // exact match okay
iTakePoint2D(point3D); // extra information okay
iTakePoint2D({ x: 0 }); // Error: missing information `y`