src/vs/base/common/skipList.ts/SkipList/forEach
class SkipList:	forEach(callbackfn: (value: V, key: K, map: Map<K, V>) => void, thisArg?: any): void {
		let node = this._header.forward[0];
		while (node) {
			callbackfn.call(thisArg, node.value, node.key, this);
			node = node.forward[0];
		}
	}