purify

var app = express(),
    purify = require('purify');

app.get('/:userId', function (req, res, next) {
    var userId = purify.positiveInteger(req.param('userId')),
        force = purify.boolean(req.param('force'), true);

    if (userId) {
        // ...
    } else {
        res.send(400);
    }
});

API

• .email(rawValue, defaultValue)

• .emailIdn(rawValue, defaultValue) - Returns e-mail with non-punycoded form regardless of input.

• .domainName(rawValue, defaultValue)

• .domainNameIdn(rawValue, defaultValue) - Returns domain in non-punycoded form regardless of input.

• .url(rawValue, defaultValue)

• .urlWithLocalhost(rawValue, defaultValue)

• .integer(rawValue, defaultValue)

• .integerInRange(rawValue, lower, upper, defaultValue)

• .positiveInteger(rawValue, defaultValue)

• .positiveIntegerOrZero(rawValue, defaultValue)

• .float(rawValue, defaultValue)

• .positiveFloat(rawValue, defaultValue)

• .positiveFloatOrZero(rawValue, defaultValue)

• .nonEmptyVisibleUnicode(rawValue, defaultValue)

• .visibleUnicode(rawValue, defaultValue)

• .nonEmptyPrintableUnicode(rawValue, defaultValue)

• .printableUnicode(rawValue, defaultValue)

• .nonEmptyVisibleAscii(rawValue, defaultValue)

• .visivleAscii(rawValue, defaultValue)

• .nonEmptyPrintableAscii(rawValue, defaultValue)

• .printableAscii(rawValue, defaultValue)

• .alphaNumeric(rawValue, defaultValue)

• .nonEmptyAlphaNumeric(rawValue, defaultValue)

• .alphaNumericWithDot(rawValue, defaultValue)

• .uuid(rawValue, defaultValue)

• .upperCaseUuid(rawValue, defaultValue)

• .lowerCaseUuid(rawValue, defaultValue)

• .json(rawValue, defaultValue)

Mostly, you can leave defaultValue empty, which will cause purify to return undefined in case the value doesn't pass validation.