JSFiddle - React, Tailwind, and code Playground

HTML

<p id="demo"></p>

JavaScript

var rooms = {};
            rooms['test'] = {
                players: {},
                drawer: {},
                answer: '',
                msgHistory: [],
                drawingHistory: [],
                msgNum: 0,
                pixelNum: 0,
                settings: {
                    maxPlayers: 12,
                    gameMode: 'drawingAndGuess'
                }
            };

            var room = rooms['test'],
                msgHistory = room.msgHistory,
                msgNum = room.msgNum,
                drawingHistory = room.drawingHistory,
                pixelNum = room.pixelNum;

            var expTimes = 10000000;
            //不存入變數1
            alert('不存入變數速度測試1開始')
            start = Date.now();
            for (let i=0;i<expTimes;i++){
                rooms['test'].drawingHistory[rooms['test'].pixelNum-1] = i;
            }
            end = Date.now();
            timeA1 = (end - start)/1000;
            alert('不存入變數速度測試1結束，耗時 ' + timeA1 + '秒');

            //存入變數
            alert('存入變數速度測試開始')
            start = Date.now();
            for (let i=0;i<expTimes;i++){
                drawingHistory[pixelNum-1] = i;
            }
            end = Date.now();
            timeB = (end - start)/1000;
            alert('存入變數速度測試結束，耗時 ' + timeB + '秒');
            //不存入變數2
            alert('不存入變數速度測試2開始')
            start = Date.now();
            for (let i=0;i<expTimes;i++){
                rooms['test'].drawingHistory[rooms['test'].pixelNum-1] = i;
            }
            end = Date.now();
            timeA2 = (end - start)/1000;
            alert('不存入變數速度測試2結束，耗時 ' + timeA2 + '秒');
            alert('測試完成!看結果!');

            document.getElementById('demo').innerHTML = '不存入變數耗時: ' + timeA1 + '秒<br>存入變數耗時: ' + timeB + '秒<br>不存入變數二次測試耗時: ' + timeA2 + '秒';