Function patchProperty

packages/zone.js/lib/common/utils.ts:197–300

(obj: any, prop: string, prototype?: any)

};

export function patchProperty(obj: any, prop: string, prototype?: any) {
  let desc = ObjectGetOwnPropertyDescriptor(obj, prop);
  if (!desc && prototype) {
    // when patch window object, use prototype to check prop exist or not
    const prototypeDesc = ObjectGetOwnPropertyDescriptor(prototype, prop);
    if (prototypeDesc) {
      desc = {enumerable: true, configurable: true};
    }
  }
  // if the descriptor not exists or is not configurable
  // just return
  if (!desc || !desc.configurable) {
    return;
  }

  const onPropPatchedSymbol = zoneSymbol('on' + prop + 'patched');
  if (obj.hasOwnProperty(onPropPatchedSymbol) && obj[onPropPatchedSymbol]) {
    return;
  }

  // A property descriptor cannot have getter/setter and be writable
  // deleting the writable and value properties avoids this error:
  //
  // TypeError: property descriptors must not specify a value or be writable when a
  // getter or setter has been specified
  delete desc.writable;
  delete desc.value;
  const originalDescGet = desc.get;
  const originalDescSet = desc.set;

  // slice(2) cuz 'onclick' -> 'click', etc
  const eventName = prop.slice(2);

  let eventNameSymbol = zoneSymbolEventNames[eventName];
  if (!eventNameSymbol) {
    eventNameSymbol = zoneSymbolEventNames[eventName] = zoneSymbol('ON_PROPERTY' + eventName);
  }

  desc.set = function (this: EventSource, newValue) {
    // In some versions of Windows, the `this` context may be undefined
    // in on-property callbacks.
    // To handle this edge case, we check if `this` is falsy and
    // fallback to `_global` if needed.
    let target = this;
    if (!target && obj === _global) {
      target = _global;
    }
    if (!target) {
      return;
    }

    const previousValue = (target as any)[eventNameSymbol];
    if (typeof previousValue === 'function') {
      target.removeEventListener(eventName, wrapFn);
    }

    // https://github.com/angular/zone.js/issues/978
    // If an inline handler (like `onload`) was defined before zone.js was loaded,