method-shorthand-jsdoc

Method Shorthand for JSDoc Preservation

When factory functions have helper functions that are only used by returned methods, move them INTO the return object using method shorthand. This ensures JSDoc comments are properly passed through to consumers.

Related Skills: See factory-function-composition for the four-zone factory anatomy and the this decision rule.

The Problem

You write a factory function with a well-documented helper:

function createHeadDoc(options: { workspaceId: string }) {
	const { workspaceId } = options;

	/**
	 * Get the current epoch number.
	 *
	 * Computes the maximum of all client-proposed epochs.
	 * This ensures concurrent bumps converge to the same version.
	 *
	 * @returns The current epoch (0 if no bumps have occurred)
	 */
	function getEpoch(): number {
		let max = 0;
		for (const value of epochsMap.values()) {
			max = Math.max(max, value);
		}
		return max;
	}

	return {
		workspaceId,
		getEpoch, // JSDoc is NOT visible when hovering on returned object!

		bumpEpoch(): number {
			const next = getEpoch() + 1; // Calling internal helper
			return next;
		},
	};
}

When you hover over head.getEpoch() in your IDE, you see... nothing. The JSDoc is lost.

The Solution

Move the helper INTO the return object using method shorthand:

function createHeadDoc(options: { workspaceId: string }) {
	const { workspaceId } = options;

	return {
		workspaceId,

		/**
		 * Get the current epoch number.
		 *
		 * Computes the maximum of all client-proposed epochs.
		 * This ensures concurrent bumps converge to the same version.
		 *
		 * @returns The current epoch (0 if no bumps have occurred)
		 */
		getEpoch(): number {
			let max = 0;
			for (const value of epochsMap.values()) {
				max = Math.max(max, value);
			}
			return max;
		},

		bumpEpoch(): number {
			const next = this.getEpoch() + 1; // Use this.methodName()
			return next;
		},
	};
}

Now hovering over head.getEpoch() shows the full JSDoc.

This matters even more when the public type derives from the factory:

export type HeadDoc = ReturnType<typeof createHeadDoc>;

With ReturnType, the returned object is the public type source. Put consumer-facing JSDoc directly on the returned method or getter so hover, completion, and Go to Definition all land on the same member.

JSDoc preservation and Go-to-Definition flow from the same choice: where the consumer's tools resolve to. Method shorthand in zone 4 keeps both on the real definition. A hand-written interface annotation, a destructure-re-export of a module-level object, or a wrapper that just re-emits a function are the regressions that split them apart. See typescript "Go-to-Definition Awareness" for the navigation-side rules.

Why This Works

1. JSDoc attaches to the method definition site - when methods are inline in the return object, the JSDoc is directly on the property TypeScript sees
2. Method shorthand uses function semantics - this is bound to the object, so this.getEpoch() works
3. No separate helper needed - if it's only used by sibling methods, it belongs in the same object

The Pattern

// BAD: Helper defined separately, JSDoc lost on return
function createService(client) {
  /** Fetches user data with caching. */
  function fetchUser(id: string) { ... }

  return {
    fetchUser,  // JSDoc not visible to consumers!
    getProfile(id: string) {
      return fetchUser(id);  // Works, but consumers can't see docs
    },
  };
}

// GOOD: Method shorthand, JSDoc preserved
function createService(client) {
  return {
    /** Fetches user data with caching. */
    fetchUser(id: string) { ... },

    getProfile(id: string) {
      return this.fetchUser(id);  // Use this.method()
    },
  };
}

Decision Rule

Move a helper into the returned object when it is only used by returned methods, consumers need hover JSDoc on that method, and the helper does not run during initialization.

Keep helpers separate when they are called before return, shared across factories, or truly internal and not exposed.

Arrow Functions Don't Work

Arrow functions don't have their own this:

// BAD: Arrow function, this is undefined
return {
  getEpoch: () => { ... },
  bumpEpoch: () => {
    this.getEpoch();  // ERROR: this is undefined!
  },
};

// GOOD: Method shorthand has correct this binding
return {
  getEpoch() { ... },
  bumpEpoch() {
    this.getEpoch();  // Works!
  },
};

Real Example

From packages/epicenter/src/core/docs/head-doc.ts:

export function createHeadDoc(options: { workspaceId: string; ydoc?: Y.Doc }) {
	const { workspaceId } = options;
	const ydoc = options.ydoc ?? new Y.Doc({ guid: workspaceId });
	const epochsMap = ydoc.getMap<number>('epochs');

	return {
		ydoc,
		workspaceId,

		/**
		 * Get the current epoch number.
		 *
		 * Computes the maximum of all client-proposed epochs.
		 * This ensures concurrent bumps converge to the same version
		 * without skipping epoch numbers.
		 *
		 * @returns The current epoch (0 if no bumps have occurred)
		 */
		getEpoch(): number {
			let max = 0;
			for (const value of epochsMap.values()) {
				max = Math.max(max, value);
			}
			return max;
		},

		/**
		 * Bump the epoch to the next version.
		 *
		 * @returns The new epoch number after bumping
		 */
		bumpEpoch(): number {
			const next = this.getEpoch() + 1;
			epochsMap.set(ydoc.clientID.toString(), next);
			return next;
		},

		// ... other methods using this.getEpoch()
	};
}

Summary

Method shorthand is the only approach that preserves JSDoc AND allows methods to call each other via this.

Where This Fits in the Factory Function Anatomy

Factory functions follow a four-zone internal shape: immutable state → mutable state → private helpers → return object. Method shorthand lives in the return object (zone 4): the public API.

The this.method() vs direct-call decision depends on which zone the function lives in:

When a helper needs to be in zone 3, its JSDoc won't be visible to consumers; that's correct, because it's a private implementation detail. Only zone 4 methods need consumer-facing JSDoc.

See Closures Are Better Privacy Than Keywords for the full factory function anatomy.

References

• docs/articles/method-shorthand-jsdoc-preservation.md - Same content as article
• docs/articles/closures-are-better-privacy-than-keywords.md - Factory function anatomy and zone system