Javascript根据另一个下拉框值更改下拉框选项

Question

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Answer 1

这是一个简单的示例，可以帮助您入门。

它的工作原理是将 change 事件的事件监听器附加到省下拉列表，然后通过 provs 对象查找该省的城镇。

查看评论以了解每一行的详细解释。

window.onload = function() {
  // provs is an object but you can think of it as a lookup table
  var provs = {
        'British Columbia': ['Victoria', 'Sanitch'],
        'Ontario': ['Bracebridge', 'Waterloo']
      },
      // just grab references to the two drop-downs
      prov_select = document.querySelector('#prov'),
      town_select = document.querySelector('#town');

  // populate the provinces drop-down
  setOptions(prov_select, Object.keys(provs));
  // populate the town drop-down
  setOptions(town_select, provs[prov_select.value]);
  
  // attach a change event listener to the provinces drop-down
  prov_select.addEventListener('change', function() {
    // get the towns in the selected province
    setOptions(town_select, provs[prov_select.value]);
  });
    
  function setOptions(dropDown, options) {
    // clear out any existing values
    dropDown.innerHTML = '';
    // insert the new options into the drop-down
    options.forEach(function(value) {
      dropDown.innerHTML += '<option name="' + value + '">' + value + '</option>';
    });
  }  
};

<select id="prov"></select>
<select id="town"></select>