MockAxios with call operator support

axios.js

const defaultResponse = { data: {} };

class ExtensibleFunction extends Function {
  constructor(f) {
    return Object.setPrototypeOf(f, new.target.prototype);
  }
}

export class MockAxios extends ExtensibleFunction {
  static instances = new WeakMap();
  static defaultInstance;

  static resetAll(clear = true) {
    if (clear) {
      // Getting the defaultInstance to be able to set it in the new WeakMap
      const defaultInstancePrivateMembers = MockAxios.instances.get(
        MockAxios.defaultInstance
      );
      MockAxios.instances = new WeakMap();
      MockAxios.instances.set(
        MockAxios.defaultInstance,
        defaultInstancePrivateMembers
      );
      MockAxios.reset(MockAxios.defaultInstance);
    } else {
      MockAxios.instances.entries().forEach((instance) => {
        MockAxios.reset(instance);
      });
    }
  }

  static reset(instance) {
    instance.get = jest.fn(() => Promise.resolve(defaultResponse));
    instance.put = jest.fn(() => Promise.resolve(defaultResponse));
    instance.post = jest.fn(() => Promise.resolve(defaultResponse));
    instance.delete = jest.fn(() => Promise.resolve(defaultResponse));

    const privateMembers = MockAxios.instances.get(instance);
    privateMembers.__callee = jest.fn(() => Promise.resolve(defaultResponse));

    MockAxios.addMockingFeatures(privateMembers.__callee, instance);
  }

  static addMockingFeatures(source, target) {
    // Adding mocking properties to the axios function
    Object.entries(source).forEach(([k, v]) => {
      if (typeof v === 'function') {
        target[k] = v.bind(source);
      } else {
        target[k] = v;
      }
    });
  }

  constructor(defaults = { headers: { common: {} } }) {
    // privateMembers: All the stuff that has to be hidden because it is not normally on axios.
    //   __callee: the mock function that will be called when one does `axios(...args)`
    const privateMembers = {
      __callee: null,
    };

    // This closure allows the __callee member of privateMembers to be
    // modified dynamically, thus ensuring the ability to reset the instance
    super(function(...args) {
      return privateMembers.__callee(...args);
    });
    // We set it in a WeakMap to be able to set/reset __callee later on
    // By not setting __callee to a function, we avoid having the 'this' current object from being
    // set in the scope of the function, which would prevent the WeakMap from releasing it
    MockAxios.instances.set(this, privateMembers);

    const self = this;
    this.defaults = defaults;
    MockAxios.reset(self);
  }

  create(options) {
    return new MockAxios(options);
  }
}

// ////////////////////////////////////////////////

const defaultInstance = new MockAxios();
MockAxios.defaultInstance = defaultInstance;

export default defaultInstance;