If the number is greater than 1e+21 (including) or less than 1e-7 (including), it will return 1. (when using radix/base 10).

e.g.

console.log(parseInt(0.0000001));
console.log(parseInt(0.000000123));
console.log(parseInt(1e-7));
console.log(parseInt(1e+21));

checkout mdn documantation:

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/parseInt#examples