Meteor - 在选择更改时更新 var [英] Meteor - update var on select change

问题描述

我有一个下拉菜单，但是当用户选择另一个值时，我想要执行一些代码.我的问题:如何检查下拉列表的选定值是否已更改?

I've got a dropdown, but when a user select another value, I want some code to be executed. My question: How can I check whether the selected value of the dropdown has changed?

在我的 html 文件中:

In my html file:

<template name="jaren">    
    <form id="yearFilter">
        <select class="selectpicker span2" id="yearpicker" >
            {{#each jaren}}
                {{#if selectedYear}}
                <option selected value="{{_id}}">{{jaar}} {{description}}</option>
                {{else}}
                <option value="{{_id}}">{{jaar}} {{description}}</option>
                {{/if}}
            {{/each}}
        </select> 
    </form>
</template>

在我的 javascript 文件中:

in my javascript file:

Template.jaren.jaren = function() {
  return Years.find();
}
Template.jaren.selectedYear = function() {
  if (Session.get('year_id') == this._id) {
    return true;
  } else {
    return false;
  }
}
Template.jaren.events({
  'change form#yearFilter #yearpicker': function(event, template) {
    Session.set('year_id', template.find('#yearpicker').value);
    console.log("value changed");
  }
});

推荐答案

您可以在事件处理程序中获取 select 元素的值，然后将其与您已经存储的旧值进行比较:

You can get the value of the select element inside the event handler and then compare it to the old value you had already stored:

"change #yearpicker": function(evt) {
  var newValue = $(evt.target).val();
  var oldValue = Session.get("year_id");
  if (newValue != oldValue) {
    // value changed, let's do something
  }
  Session.set("year_id", newValue);
}

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