JiBrok, message field, JavaScript Example: update message on create.

update message on create.js

require(['jquery'], function($) {
	function setCFValue(customfield_id, value){
		$('#' + customfield_id).val(value).trigger('change')
	}

	function setMessage(title, body, messageType){
		var jsonMessage = {}
		jsonMessage.title = title
		jsonMessage.body = body
		jsonMessage.messageType = messageType
		setCFValue(CF_ID_MESSAGE, JSON.stringify(jsonMessage))
	}
	
	//EDIT HERE
	var CF_ID_MESSAGE = 'customfield_10200'

	setMessage('New title', 
		'Loooong <br>'+
		'Loooong<br>'+
		'Loooong<br>'+
		'message', 
		'error')//info, success, warning, error, change, SIMPLE_VIEW
})