any-nesting-mock.ts

/**
 * Allows arbitrary level property access and callable,
 * support mock with usage likes:
 * ```
 * faker = new FakeClass()
 * faker.xxxx()
 *
 * faker()
 *
 * {...faker()}
 *
 * faker.xxx()
 *
 * faker[xxx].xxx()
 * ```
 */
export const anyNestingMock = () => new Proxy(
  /**
   * make self callable with `[[Call]]` and `[[Construct]]` internal method
   * by proxy target as a function object
   * https://tc39.es/ecma262/#sec-ecmascript-function-objects-call-thisargument-argumentslist
   */
  function () {},
  {
    /** https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Proxy/Proxy/construct */
    construct: () => anyNestingMock(),
    /** https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Proxy/Proxy/apply */
    apply: () => anyNestingMock(),
    get: (target, prop) => {

      if (prop === Symbol.toPrimitive) return () => ''
      return anyNestingMock()
    },
  },
)

const instance1 = anyNestingMock()
const instance2 = anyNestingMock()

// unit test for the mocker of anyNestingMock
assert(instance1())
assert(new instance1())
assert({ ...instance1() })
assert(instance1.xxx())
assert({ ...instance1.xxx() })
assert(instance1[instance2].xxx())