this._ids = new Map([ // mapping from JS values to reference ids
				[0, 1],
				[null, 2],
				[true, 3],
				[false, 4],
				[globalThis, 5],
				[this, 6],
			]);
			this._idPool = [];   // unused ids that have been garbage collected
			this.exited = false; // whether the Go program has exited