13     key: string;
20   key: string;
33   getItemByKey: (key: string) => StackItem<T> | null;
55     const key = '' + count;  constant
57     keys.push(key);
60       pushResolvers[key] = resolve;
64       key,
69       pop: () => pop(`${key}`),
70       onPushEnd: () => onPushEnd(key),
71       onPopEnd: () => onPopEnd(key),
79     lookup[key] = item;
81     emit('pushstart', key);
86   function onPushEnd(key: string) {
87     const item = lookup[key];  constant
92       const resolver = pushResolvers[key];  constant
95         resolver(getItemByKey(key));
96         delete pushResolvers[key];
99       emit('pushend', key);
109       const key = amount;  constant
110       const item = lookup[key];  constant
114           onPushEnd(key);
120           popResolvers[key] = resolve;
125         emit('popstart', key);
140       const key = keys[i];  constant
141       const item = lookup[key];  constant
150       const key = keys[i];  constant
151       const item = lookup[key];  constant
155           onPushEnd(key);
161           popResolvers[key] = resolve;
166         emit('popstart', key);
174   function onPopEnd(key: string) {
175     const item = lookup[key];  constant
176     keys = keys.filter((k) => k !== key);
178     const resolver = popResolvers[key];  constant
181       resolver(getItemByKey(key));
182       delete popResolvers[key];
186     emit('popend', key);
199   function emit(action: StackAction, key: string) {
202       const event = { key, action };
207   function getItemByKey(key: string) {
208     return lookup[key];
212     const items = keys.map((key) => lookup[key]);