73 lines
3.0 KiB
JavaScript
73 lines
3.0 KiB
JavaScript
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const copyProperty = (to, from, property, ignoreNonConfigurable) => {
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// `Function#length` should reflect the parameters of `to` not `from` since we keep its body.
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// `Function#prototype` is non-writable and non-configurable so can never be modified.
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if (property === 'length' || property === 'prototype') {
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return;
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}
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// `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.
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if (property === 'arguments' || property === 'caller') {
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return;
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}
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const toDescriptor = Object.getOwnPropertyDescriptor(to, property);
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const fromDescriptor = Object.getOwnPropertyDescriptor(from, property);
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if (!canCopyProperty(toDescriptor, fromDescriptor) && ignoreNonConfigurable) {
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return;
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}
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Object.defineProperty(to, property, fromDescriptor);
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};
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// `Object.defineProperty()` throws if the property exists, is not configurable and either:
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// - one its descriptors is changed
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// - it is non-writable and its value is changed
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const canCopyProperty = function (toDescriptor, fromDescriptor) {
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return toDescriptor === undefined || toDescriptor.configurable || (
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toDescriptor.writable === fromDescriptor.writable
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&& toDescriptor.enumerable === fromDescriptor.enumerable
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&& toDescriptor.configurable === fromDescriptor.configurable
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&& (toDescriptor.writable || toDescriptor.value === fromDescriptor.value)
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);
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};
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const changePrototype = (to, from) => {
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const fromPrototype = Object.getPrototypeOf(from);
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if (fromPrototype === Object.getPrototypeOf(to)) {
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return;
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}
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Object.setPrototypeOf(to, fromPrototype);
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};
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const wrappedToString = (withName, fromBody) => `/* Wrapped ${withName}*/\n${fromBody}`;
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const toStringDescriptor = Object.getOwnPropertyDescriptor(Function.prototype, 'toString');
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const toStringName = Object.getOwnPropertyDescriptor(Function.prototype.toString, 'name');
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// We call `from.toString()` early (not lazily) to ensure `from` can be garbage collected.
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// We use `bind()` instead of a closure for the same reason.
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// Calling `from.toString()` early also allows caching it in case `to.toString()` is called several times.
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const changeToString = (to, from, name) => {
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const withName = name === '' ? '' : `with ${name.trim()}() `;
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const newToString = wrappedToString.bind(null, withName, from.toString());
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// Ensure `to.toString.toString` is non-enumerable and has the same `same`
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Object.defineProperty(newToString, 'name', toStringName);
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const {writable, enumerable, configurable} = toStringDescriptor; // We destructue to avoid a potential `get` descriptor.
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Object.defineProperty(to, 'toString', {value: newToString, writable, enumerable, configurable});
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};
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export default function mimicFunction(to, from, {ignoreNonConfigurable = false} = {}) {
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const {name} = to;
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for (const property of Reflect.ownKeys(from)) {
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copyProperty(to, from, property, ignoreNonConfigurable);
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}
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changePrototype(to, from);
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changeToString(to, from, name);
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return to;
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}
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