How to write a drop-down form using javascript

With the continuous development of Internet technology, dynamic interactive web pages are becoming more and more popular among users. As one of the commonly used form elements, the drop-down box is still the same no matter how its style changes. constant. In this article, I will introduce how to write a drop-down form in JavaScript.

1. Basic structure:

The most basic structure of the drop-down form should be a tag and multiple tags. The basic structure of the drop-down form is as follows:

<select id="dropdown">
  <option value="">请选择</option>
  <option value="1">选项一</option>
  <option value="2">选项二</option>
  <option value="3">选项三</option>
  <option value="4">选项四</option>
</select>

2. Implement the drop-down form:

1. Get the drop-down form through DOM:

First, we need to get

The label can be obtained through the getElementById method of the JavaScript document object:

var dropdown = document.getElementById("dropdown");

2. Implement the drop-down form through event monitoring:

Next we need to implement the function of the drop-down box. When the user is in When an option is selected in the drop-down box, we need to respond to the event and get the selected value.

dropdown.addEventListener("change", function() {
  var value = dropdown.options[dropdown.selectedIndex].value;
  console.log(value); 
});

3. Add options dynamically:

Sometimes, we need to add options dynamically. In JavaScript, we can use the createElement and appendChild methods to dynamically add tags:

var option = document.createElement("option");
option.text = "选项五";
option.value = "5";

dropdown.appendChild(option);

3. Complete code:

<select id="dropdown">
  <option value="">请选择</option>
  <option value="1">选项一</option>
  <option value="2">选项二</option>
  <option value="3">选项三</option>
  <option value="4">选项四</option>
</select>

<script>
  var dropdown = document.getElementById(&quot;dropdown&quot;);
  
  dropdown.addEventListener("change", function() {
    var value = dropdown.options[dropdown.selectedIndex].value;
    console.log(value);  
  });
  
  var option = document.createElement("option");
  option.text = "选项五";
  option.value = "5";
  
  dropdown.appendChild(option);
</script>

4. Summary:

Use Writing drop-down forms in JavaScript is a basic front-end development technology, which can help us achieve complex interactive effects and also allow us to better enhance the interactivity of the page. Through studying this article, I believe you have learned how to use JavaScript to write drop-down forms.

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