javascript：评估用户输入的密码的强度

// Password strength meter
function passwordStrength(password1, username, password2) {
var shortPass = 1,
badPass = 2,
goodPass = 3,
strongPass = 4,
mismatch = 5,
symbolSize = 0,
natLog, score;

// password 1 != password 2
if ((password1 != password2) && password2.length > 0)
return mismatch
//password < 4
if (password1.length < 4)
return shortPass
//password1 == username
if (password1.toLowerCase() == username.toLowerCase())
return badPass;

if (password1.match(/[0-9]/))
symbolSize += 10;
if (password1.match(/[a-z]/))
symbolSize += 26;
if (password1.match(/[A-Z]/))
symbolSize += 26;
if (password1.match(/[^a-zA-Z0-9]/))
symbolSize += 31;

natLog = Math.log(Math.pow(symbolSize, password1.length));
score = natLog / Math.LN2;

if (score < 40)
return badPass
if (score < 56)
return goodPass

return strongPass;
}