makeSchema.js

// Validator will pass a form to schema creator
export default form => ({
  type: 'object',
  properties: {
    text: {
      type: 'string',
      messages: {
        type: 'Should be a string',
        required: 'Please enter a text',
      },
    },
    minimum: {
      type: 'integer',
      // form data can be used to set schema props explicitly
      maximum: form.maximum,
      minimum: 0,
      messages: {
        type: 'Should be a zero or more',
        minimum: 'Should exceed 0',
      },
    },
    maximum: {
      default: null,
      type: ['integer', 'null'],
      minimum: { $data: '1/minimum' },
      // Messages key is not a part of json.org spec,
      // but it is very useful in real life
      messages: {
        type: 'Should be a zero or more',
        minimum: `Should exceed ${form.minimum || 0}`,
      },
    },
  },
  required: ['text', 'minimum'],
});