Javascript 从下拉列表中获取值到textarea JS

我有一个下拉列表，可以从表单生成器中获取字段，在下拉列表的正下方有一个文本区域。我希望将下拉列表中的值放入当前光标位置所在的文本区域。这与检测下拉列表中的变化有关

任何帮助都将不胜感激，因为我一直在努力解决这个问题

    define(["jquery", "underscore", "backbone", "text!templates/app/tab-nav-actions.html", "text!templates/app/textbox.html", "text!templates/app/textarea.html", "views/select", "helper/pubsub"],
function($, _, Backbone, _tabNavTemplate, _textboxTemplate, _textareaTemplate,Select, PubSub) {
    return Backbone.View.extend({
        tagName: "div",
        className: "tab-pane col-xs-12 col-sm-12 col-md-12 col-lg-12",
        initialize: function() {
            this.id = this.options.id.toLowerCase().replace(/\W/g, '');
            this.id = this.id;
            this.tabNavTemplate = _.template(_tabNavTemplate);
            this.textboxTemplate = _.template(_textboxTemplate);
            this.textareaTemplate = _.template(_textareaTemplate);
            this.select = new Select({
                id: this.id  + (new Date().getTime() - 2),
                collection: this.collection,
                className: "col-xs-6 col-sm-6 col-md-5 col-lg-4 col-md-offset-1 col-lg-offset-1"
            });
            this.drop = new Select({
                id: this.id  + (new Date().getTime() - 2),
                collection: this.collection,
                className: "col-xs-6 col-sm-6 col-md-5 col-lg-4 col-md-offset-1 col-lg-offset-1"
            });
            this.render();
        },
        render: function() {
            $("#actionstabs").append(this.tabNavTemplate({
                title: this.options.title,
                id: this.id
            }));
            this.$el.attr("id", this.id);
            this.$el.append("<div class='actionsheadingrow col-xs-12 col-sm-12 col-md-12 col-lg-12'><h2>To</h2></div>");
            this.$el.append(this.select.render().el);
            this.$el.append("<div class='col-xs-12 col-sm-12 col-md-12 col-lg-12'><h2>Subject</h2></div>");
            this.$el.append(this.textboxTemplate({
                subjectclasses: "col-xs-6 col-sm-6 col-md-5 col-lg-4 col-md-offset-1 col-lg-offset-1",
                id: this.id + "subject"
            }));
            this.$el.append("<div class='col-xs-12 col-sm-12 col-md-12 col-lg-12'><h3>Message</h3></div>");
            this.$el.append(this.textareaTemplate({
                bodyclasses: "col-xs-6 col-sm-6 col-md-8 col-lg-4 col-md-offset-1 col-lg-offset-1",
                id: this.id + "Message"
            }));
            this.$el.append(this.drop.render().el);
            this.$el.appendTo("#actionscontent");
            this.delegateEvents();
        }
    });
    drop.onchange = function(){
          textareaTemplate.value = textareaTemplate.value  + this.append; //to appened
         //mytextbox.innerHTML = this.value;
    }
});

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我建议看一个级联下拉列表。从中，您可以提取更改事件并获取下拉列表的值。然后您需要做的就是设置文本区域的文本。像这样的