const a = Array.from({length: 1000}).map((_, i)=>`${i}`);
const b = Array.from({length: 2000}).map((_, i)=>`${i}`);
const aSmall = ['a', 'b', 'c', 'd'];
const bSmall = ['e', 'f', 'g', 'h', 'i'];
const c = [...a, ...b];
const c = a.concat(b)
const c = [...aSmall, ...bSmall];
const c = aSmall.concat(bSmall)