@cjs-mifi-test/mimic-fn/index.js

CJS version: Make a function mimic another one

"use strict";

Object.defineProperty(exports, "__esModule", {
  value: true
});
exports.default = mimicFunction;

const copyProperty = (to, from, property, ignoreNonConfigurable) => {
  // `Function#length` should reflect the parameters of `to` not `from` since we keep its body.
  // `Function#prototype` is non-writable and non-configurable so can never be modified.
  if (property === 'length' || property === 'prototype') {
    return;
  } // `Function#arguments` and `Function#caller` should not be copied. They were reported to be present in `Reflect.ownKeys` for some devices in React Native (#41), so we explicitly ignore them here.


  if (property === 'arguments' || property === 'caller') {
    return;
  }

  const toDescriptor = Object.getOwnPropertyDescriptor(to, property);
  const fromDescriptor = Object.getOwnPropertyDescriptor(from, property);

  if (!canCopyProperty(toDescriptor, fromDescriptor) && ignoreNonConfigurable) {
    return;
  }

  Object.defineProperty(to, property, fromDescriptor);
}; // `Object.defineProperty()` throws if the property exists, is not configurable and either:
// - one its descriptors is changed
// - it is non-writable and its value is changed


const canCopyProperty = function (toDescriptor, fromDescriptor) {
  return toDescriptor === undefined || toDescriptor.configurable || toDescriptor.writable === fromDescriptor.writable && toDescriptor.enumerable === fromDescriptor.enumerable && toDescriptor.configurable === fromDescriptor.configurable && (toDescriptor.writable || toDescriptor.value === fromDescriptor.value);
};

const changePrototype = (to, from) => {
  const fromPrototype = Object.getPrototypeOf(from);

  if (fromPrototype === Object.getPrototypeOf(to)) {
    return;
  }

  Object.setPrototypeOf(to, fromPrototype);
};

const wrappedToString = (withName, fromBody) => `/* Wrapped ${withName}*/\n${fromBody}`;

const toStringDescriptor = Object.getOwnPropertyDescriptor(Function.prototype, 'toString');
const toStringName = Object.getOwnPropertyDescriptor(Function.prototype.toString, 'name'); // We call `from.toString()` early (not lazily) to ensure `from` can be garbage collected.
// We use `bind()` instead of a closure for the same reason.
// Calling `from.toString()` early also allows caching it in case `to.toString()` is called several times.

const changeToString = (to, from, name) => {
  const withName = name === '' ? '' : `with ${name.trim()}() `;
  const newToString = wrappedToString.bind(null, withName, from.toString()); // Ensure `to.toString.toString` is non-enumerable and has the same `same`

  Object.defineProperty(newToString, 'name', toStringName);
  Object.defineProperty(to, 'toString', { ...toStringDescriptor,
    value: newToString
  });
};

function mimicFunction(to, from, {
  ignoreNonConfigurable = false
} = {}) {
  const {
    name
  } = to;

  for (const property of Reflect.ownKeys(from)) {
    copyProperty(to, from, property, ignoreNonConfigurable);
  }

  changePrototype(to, from);
  changeToString(to, from, name);
  return to;
}