const arr = [] for (let i = 0; i < 200000; i++) { arr.push(i) } let newArr = [] function run() { newArr = newArr.concat(arr) } let clearRun document.querySelector('#run').onclick = function () { clearRun = setInterval(() => { run() }, 1000) } document.querySelector('#stop').onclick = function () { clearInterval(clearRun) }