Function has

packages/svelte/src/internal/client/proxy.js:224–258

(target, prop)

		},

		has(target, prop) {
			if (prop === STATE_SYMBOL) {
				return true;
			}

			var s = sources.get(prop);
			var has = (s !== undefined && s.v !== UNINITIALIZED) || Reflect.has(target, prop);

			if (
				s !== undefined ||
				(active_effect !== null && (!has || get_descriptor(target, prop)?.writable))
			) {
				if (s === undefined) {
					s = with_parent(() => {
						var p = has ? proxy(target[prop]) : UNINITIALIZED;
						var s = source(p, stack);

						if (DEV) {
							tag(s, get_label(path, prop));
						}

						return s;
					});

					sources.set(prop, s);
				}

				var value = get(s);
				if (value === UNINITIALIZED) {
					return false;
				}
			}

			return has;
		},

		set(target, prop, value, receiver) {
			var s = sources.get(prop);