Example: Conditionally require minimum data for calls based on first parameter

conditional-types.ts

/**
 * Conditionally require additional data for function calls based on first parameter
 * Allows a union of possible interfaces that describe a minimum amount of data required
 * Values not named may still be used and have no minimum amount of data
 *
 * Extending on the work by David Sheldrick in https://artsy.github.io/blog/2018/11/21/conditional-types-in-typescript/
 */

interface BaseShape {
  name: string;
  data?: Record<string, unknown>;
}

interface Circle extends BaseShape {
  name: "circle";
  data: {
    radius: number;
    [key: string]: unknown;
  };
}

interface Rectangle extends BaseShape {
  name: "rectangle";
  data: {
    height: number;
    width: number;
    [key: string]: unknown;
  };
}

type DefinedShape = Circle | Rectangle;

const shapes: BaseShape[] = [];

type FilterByName<Shape, Name> = Shape extends { name: Name } ? Shape : never;

export function createShape<T extends DefinedShape["name"]>(
  shapeName: T,
  shapeProperties: FilterByName<DefinedShape, T>["data"]
): void;
export function createShape<T extends BaseShape["name"]>(
  shapeName: Exclude<T, DefinedShape["name"]>,
  shapeProperties?: BaseShape["data"]
): void;
export function createShape(
  shapeName: BaseShape["name"],
  shapeProperties?: BaseShape["data"]
) {
  const shape = { name: shapeName, data: shapeProperties };
  shapes.push(shape);
}

// SHOULD Pass
createShape("circle", { radius: 1 });
createShape("rectangle", { height: 3, width: 4 });
createShape("rectangle", { height: 3, width: 4, color: "red" }); // Additional fields
createShape("triangle", { height: 2 }); // Unknown shape
createShape("triangle"); // Unknown with no data

// SHOULD Error
// @ts-expect-error
createShape("circle", { height: 2, width: 3 });
// @ts-expect-error
createShape("circle", { banana: 2 });
// @ts-expect-error
createShape("rectangle", { radius: 5 });
// @ts-expect-error
createShape("rectangle", { height: 5 });
// @ts-expect-error
createShape("rectangle", {});
// @ts-expect-error
createShape("rectangle");