Builder

A constructor with twelve optional parameters

`new Request(url, method, headers, body, timeout, retries, null, null, true, false, ...)` is unreadable and error-prone — it's easy to pass arguments in the wrong order, and most callers only need a handful of them set.

Chain small, named steps

A builder exposes one method per optional piece, each returning the builder itself so calls can chain. A final `build()` assembles the immutable result. Only the fields that were actually set get used.

Fluent request builder

Every `.with...()` call returns `this`, so calls chain naturally. `build()` is the single point where the final object is produced.

class RequestBuilder {
  #config = { method: "GET", headers: {}, timeout: 5000 };

  withUrl(url) { this.#config.url = url; return this; }
  withMethod(method) { this.#config.method = method; return this; }
  withHeader(key, value) { this.#config.headers[key] = value; return this; }
  withTimeout(ms) { this.#config.timeout = ms; return this; }

  build() {
    if (!this.#config.url) throw new Error("url is required");
    return Object.freeze({ ...this.#config });
  }
}

const request = new RequestBuilder()
  .withUrl("/api/orders")
  .withMethod("POST")
  .withHeader("Content-Type", "application/json")
  .withTimeout(3000)
  .build();

console.log(request);

Trade-offs

• Readable at the call site — Each step is named, so the order and meaning of arguments is obvious without checking docs.
• Partial construction is safe — Fields nobody sets keep sensible defaults instead of requiring null placeholders.
• Extra ceremony for simple objects — If an object only ever has two or three fields, a plain object literal is simpler.