@wordpress/interactivity/build-module/proxies/context.js

Package that provides a standard and simple way to handle the frontend interactivity of Gutenberg blocks.

const contextObjectToProxy = new WeakMap();
const contextObjectToFallback = new WeakMap();
const contextProxies = new WeakSet();
const descriptor = Reflect.getOwnPropertyDescriptor;

// TODO: Use the proxy registry to avoid multiple proxies on the same object.
const contextHandlers = {
  get: (target, key) => {
    const fallback = contextObjectToFallback.get(target);
    // Always subscribe to prop changes in the current context.
    const currentProp = target[key];

    /*
     * Return the value from `target` if it exists, or from `fallback`
     * otherwise. This way, in the case the property doesn't exist either in
     * `target` or `fallback`, it also subscribes to changes in the parent
     * context.
     */
    return key in target ? currentProp : fallback[key];
  },
  set: (target, key, value) => {
    const fallback = contextObjectToFallback.get(target);

    // If the property exists in the current context, modify it. Otherwise,
    // add it to the current context.
    const obj = key in target || !(key in fallback) ? target : fallback;
    obj[key] = value;
    return true;
  },
  ownKeys: target => [...new Set([...Object.keys(contextObjectToFallback.get(target)), ...Object.keys(target)])],
  getOwnPropertyDescriptor: (target, key) => descriptor(target, key) || descriptor(contextObjectToFallback.get(target), key),
  has: (target, key) => Reflect.has(target, key) || Reflect.has(contextObjectToFallback.get(target), key)
};

/**
 * Wraps a context object with a proxy to reproduce the context stack. The proxy
 * uses the passed `inherited` context as a fallback to look up for properties
 * that don't exist in the given context. Also, updated properties are modified
 * where they are defined, or added to the main context when they don't exist.
 *
 * @param current   Current context.
 * @param inherited Inherited context, used as fallback.
 *
 * @return The wrapped context object.
 */
export const proxifyContext = (current, inherited = {}) => {
  if (contextProxies.has(current)) {
    throw Error('This object cannot be proxified.');
  }
  // Update the fallback object reference when it changes.
  contextObjectToFallback.set(current, inherited);
  if (!contextObjectToProxy.has(current)) {
    const proxy = new Proxy(current, contextHandlers);
    contextObjectToProxy.set(current, proxy);
    contextProxies.add(proxy);
  }
  return contextObjectToProxy.get(current);
};
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