Sometimes, you may have a long conditions to check for validity. In general, you may need to check certain thing that doesn't exists in checkit module, In that case you extends checkit module and add custom methods into it.

For ex.- To write a custom method for checking date:

To inherit a class you use:

Classname.protype.new_method = function(value) {

//The definition goes here

}

Calling the newly created method, the rule is as follows:-

const rules = {
 dob: ['required', { rule: 'date:value', message: 'dob must be a valid date.' }],
}

date:value: Here, date is the name of custom method and value is the parameter that is in user data or payload.

Code:

const checkIt = require('checkit');
Checkit.Validator.prototype.date = function date(value) {
 if (moment(value, 'MM/DD/YYYY', true).isValid() ||
  moment(value, 'MM-DD-YYYY', true).isValid()) {
  return true;
 }
 return false;
};

const payload = {name: "dinesh rawat", dob: "05/08/1988"};

const rules = {
 dob: ['required', { rule: 'date:value', message: 'dob must be a valid date.' }],
}

const checkit = new Checkit(rules);

return checkit.run(payload).then(validated => next()).then(Checkit.Error,
 err => responseObj.invalidPayload({ error: err }));