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devexamples

Type-Safe Builder Pattern

A builder that accumulates required fields in its type, refusing to compile a build call until every mandatory value has been supplied.

TypescriptConfig Management

Code

snippet
export class RequestBuilder<HasUrl extends boolean, HasMethod extends boolean> {
  private url = "";
  private method = "GET";
  private headers: Record<string, string> = {};

  static create(): RequestBuilder<false, false> {
    return new RequestBuilder<false, false>();
  }

  withUrl(this: RequestBuilder<false, HasMethod>, url: string): RequestBuilder<true, HasMethod> {
    this.url = url;
    return this as unknown as RequestBuilder<true, HasMethod>;
  }

  withMethod(this: RequestBuilder<HasUrl, false>, method: string): RequestBuilder<HasUrl, true> {
    this.method = method;
    return this as unknown as RequestBuilder<HasUrl, true>;
  }

  withHeader(key: string, value: string): this {
    this.headers[key] = value;
    return this;
  }

  build(this: RequestBuilder<true, true>): { url: string; method: string } {
    return { url: this.url, method: this.method };
  }
}

Related Examples