JSFiddle - React, Tailwind, and code Playground

JavaScript

console.time();
let str1 = '1';
const nums1 = [];
for (let i = 0; i < 10000000; i++) {
  if (str1 && Number.isInteger(+str1)) {
    nums1.push(+str1);
  }
}
console.timeEnd();

console.time();
let str2 = '1';
const nums2 = [];
for (let j = 0; j < 10000000; j++) {
  const num2 = +str2;
  if (str2 && Number.isInteger(num2)) {
    nums2.push(num2);
  }
}
console.timeEnd();