[Iv]

в таких случаях используется другой путь:

this.addNewMessage = function (new_message) {
var max_messages = 10
if (this.messages_array.length > max_messages) {
this.messages_array.shift()
}
this.messages_array.push(new_message)
return this.messages_array.join("\n")
}
.............................
this.output_txt.htmlText = this.addNewMessage(new_message)