The async validators object

asyncValidates: {
  'your-key': { // must inform this key in html attribute 'data-async-key'
    message: 'your message', // can pass by the html attribute 'data-message-error'
    fn: function(field, message, container){
      var self = this;

      // start a async validation
      this.asyncValidationStart(field, 'message during process', container);

      setTimeout(function(){ // setTimeout just to simulate a async validation

        // your logic here

        // finish a async valitation
        // the status parameter below must be boolean.
        // true means successful.
        self.asyncValidationFinish(field, message, container, status);

      }, 2000);
      
    }
  }
}

Note you must have a message and a fn keys into your async validators object. In message you configure your custom message error (you can do that using the html attribute data-message-error). In fn key you set your funciton that will validate your field asynchronously. That function will receive the field, the message error and the container as parameters.

Method asyncValidationStart()

The method asyncValidationStart starts the async validations. This method must receive as parameters the field, the process message and the container.

Method asyncValidationFinish()

The method asyncValidationFinish finishes the async validations. This method must receive as parameters the field, the error message, the container and the status of validation (true if was successful and false if was fail).

A simple example:

The javascript:

var config = {
  asyncValidates: {
    'async-block-word-java': {
      message: 'The word "java" is forbidden.',
      fn: function(field, message, container){
        var self = this;
        this.asyncValidationStart(field, 'processing...', container);
        setTimeout(function(){
          var status = (field.value !== 'java')
          self.asyncValidationFinish(field, message, container, status);
        }
      }, 2000);
    }
  }
};
var validator = new VanillaValidator(config);

The Html:

<form>
  <div>
    <input type="text" class="async" data-validate-key="async-block-word-java">
  </div>
  <div>
    <button type="submit">Send</button>
  </div>
</form>