Question

When doing validation in JavaScript, how do I keep validation methods that need to handle a bunch of contingencies from becoming unruly?

For example, I have a form with a field that has validation that checks:

• is the new value a number?
• Is the value in another field on the
  form > 0 when the current field > 0
• Is another field on the form == 1 and
  the current field == 0
• Is another field on the form == true
  and the current field is Mod another
  field == 0

Etc.

Currently, I’ve got a method with a bunch of if/else statements.

I could break each check out into it’s own method and call it from the main validation method, but that would create a ton of new methods.

Update: regardless of whether I use a framework or individual methods, am I still resigned to having the calling validation method filled with If/Else or Switch statements with alert boxes for the failing validations?

Answer 1

Sounds like you might want a rudimentary state machine. One thing you might consider is breaking the validators into the simplest forms:

function validator(op, options, pass, fail) {
    if (op(options)) {
        pass(options);
    } else {
        fail(options);
    }
}

Then you can chain them together to form more complex systems.

function isFooChecked(options) {
    return $(options.foo).is(':checked');
}

function sayHi(options) {
    alert('hi ' + options.name);
}

function fail(options) {
    alert(options.name + ' was bad');
}

function validateName() {
    validator(isFooChecked, { foo: '#someField', name: $('#nameField').val() }, sayHi, fail);
}

You’ll still have a lot of code, but if you do it right, functions should be small and easy to understand.