JSFiddle - React, Tailwind, and code Playground

HTML

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

JavaScript

var arr = [1,2,3,4,5,6,7,8,9,10,11,12,13,14];
            var expTimes = 100000000, test = 0, start = 0, end = 0, timeA1 = 0, timeB = 0, timeA2 = 0;

            //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++){
                test = arr[9];
            }
            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
            var temp = arr[9];
            alert('存入變數速度測試開始')
            start = Date.now();
            for (let i=0;i<expTimes;i++){
                test = temp;
            }
            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++){
                test = arr[9];
            }
            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';