How does parseInt() in Javascript work?

Answer 1

You only get number till where it is meaningful when converting from string to number.

console.log(parseInt('01abbb')) // 1 -> it is started by 01 before chars
console.log(parseInt('31xyz'))  // 31 -> it is started by 31 before chars
console.log(parseInt('zyz31'))  // NaN -> it is not started by numbers
console.log(parseInt('31xyz1')) // 31 -> it is started by 31 before chars