HAL Models with TypeScript 2.1

hal.ts

export type HalUrl = string;

export interface HalLink {
  href: HalUrl;
}

export interface HalObjectLinks {
  self: HalLink;
}

export interface HalObject<T extends HalObjectLinks> {
  '_links': T;
  [key: string]: any; // other properties of the object
}

export class Hal {
  public static findHref<T extends HalObjectLinks, K extends keyof T>(object: HalObject<T>, rel: K): string {
    const link = object._links ? object._links[<string>rel] : null;
    if (!link) {
      throw new Error('HAL object did not have link: ' + rel);
    }

    return link.href;
  }
}


export interface CustomerLinks extends HalObjectLinks {
  addresses: HalLink;
}

export interface Customer extends HalObject<CustomerLinks> {
  name: string;
}

const customer: Customer = <any>null;
Hal.findHref(customer, 'addresses');
// error: 'Argument of type '"users"' is not assignable to parameter of type '"self" | "addresses"'.'
Hal.findHref(customer, 'users');
Hal.findHref(customer, 'self');