Validators are implemented for each workflow execution status Validators are applied in production code

Script
function Status(status) {
  this._status = status;
  this._validators = [];
}

Status.prototype.addValidator = function(validator) {
  this._validators.push(validator);
}

Status.prototype._applyValidators = function() {
  for (var i = 0; i < this._validators.length; i++) {
    this._validators[i](this._status);
  }
}

var status = new Status('new');

//add validator
status.addValidator(function(status) {
  if (status === 'new') {
    console.log('status is new');
  }
});

//add another validator
status.addValidator(function(status) {
  if (status === 'new') {
    throw new Error('status is new');
  }
});

//execute validators
status._applyValidators();