{ status: this.step.status, dueDate: this.step.due_date }

this does not work if you are using an arrow function for assigning your data:

data: () => ({
  somevar: this.messageId // undefined
}),

Because this will not point to the component. Instead, use a plain function

data: function() {
  return { somevar: this.messageId }
},

or ES6:

data() {
    return { somevar: this.messageId }
}