createDefinedPropertyObject.ts

createDefinedPropertyObject.ts

type NonUndefined<T> = T extends undefined ? never : T;

/**
 * Create an object with a single property, if the value is not undefined.
 * Guarantees you don't have `{ myKey: undefined }` in your object.
 *
 * @param keyName the name of the key
 * @param value the value which may be undefined
 * @returns an object which should be spread into a parent object
 *
 * Usage:
 * ```ts
 * {
 *   ...createDefinedPropertyObject('myKey', myValue),
 * }
 * ```
 *
 * Results in: `{ myKey: myValue }` or `{}`, if `myValue` is undefined.
 */
function createDefinedPropertyObject<K extends string, V>(
  keyName: K,
  value: V
): { [key in K]: NonUndefined<V> } | undefined {
  return value === undefined
    ? undefined
    : ({ [keyName]: value } as { [key in K]: NonUndefined<V> });
}