How do you validate multiple items?

How do you validate multiple items in JavaScript, but without nesting ifs?

Not this...

if ( username && username.length > 2 && username.length < 45 ) {
  if ( password && password.length ... ) {
    if ( birthday && birthday.isNumeric ...) {
      if ( age && ... && ...) {
        // Success
      } else {
        // Error 4
      }
    } else {
      // Error 3     
    }
  } else {
    // Error 2
  }
} else {
  // Error 1
}

...rather, this...

validate({

  validate 'username' and use these conditions 'username && username.length...',
  validate 'password' and use these conditions 'password && password.length...',
  validate 'birthday' and use these conditions 'birthday && birthday.isNumeric...',
  validate 'age' and use these conditions 'age && ... && ...'

}, function(error) {

  if ( !error ) {
    // Success
  }

});

Do you have开发者_运维技巧 any ideas? Thanks for reply!

You can use the jQuery Validation Plugin, which will be much easier and more effective than duplicating it yourself.

I usually handle things like this like so:

var error = new Array();
var errorNum = 0;

if(!(username && username.length > 2 && ...)) {
    error[errorNum++] = "ERROR1";
}

if(!(password &&...)) {
  error[errorNum++] = "ERROR2";
}

No nesting required.

Edit: Sorry, initial syntax as PhP not javascript. I mix the two too often sometimes.