Check out example codes for "engineering adding requirements to password". It will help you in understanding the concepts better.
Code Example 1
To be honest, I find having strict password requirements to be an annoyance and not a benefit. I would say as a rule the most reasonable is to just specify a length, maybe special characters + alphanumeric. Anything more is asking for people to write down their password, which defeats the whole purpose of having secure passwords. I also hate having to change your password every x days with the usual ridiculous set of rules (e.g. cannot re-use the last 25 passwords) - again all that does is force people to write the thing down so they don't forget, at which point you might as well not ask for a password at all.
Learn ReactJs, React Native from akashmittal.com