JQuery Conditional Validation (Yes, the official documentation sucks)

Venting! jQuery Validation is a great plugin but its documentation is crap! So much cool stuff is hidden away for want of decent docs. If enough of you agree with me, I might have to write some! Watch this space. 

Anyway, I just wanted to implement some conditional validation

i.e. MAKE INPUT 'A' REQUIRED ONLY IF INPUT 'B' HAS A VALUE

And so, given two inputs with IDs InputA and InputB, the code is:

    
$(function() {
 $('#YourForm').validate({
  rules: {
   InputA : { 
    required : '#InputB:filled'
   }
  }
 });
});

You can also do this inline in your form by using declarative syntax, which I have found bugger-all documenation on!

 
<input name="InputA" type="text" data-rule-required="#InputB:filled" />
<input name="InputB" id="InputB" type="text" />

Finally, when required status is dependent on something more complicated, you can throw in a function e.g.

 
$('#myForm').validate({
 rules: {
  InputA : {
        required: function (elem) {
              // InputA is required if InputB contains 'AmazingThingy'
              return $('#InputB').val() == 'AmazingThingy';
   }
  }
 }
});