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- 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});
- };
-
- export default 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;
- }
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