How to set default value of dropdown box in Node.js

Node.js is a JavaScript runtime environment based on the Chrome V8 engine. It can be used for both server-side programming and command line tools. This technology is efficient, powerful, and easy to develop, so it is widely welcomed by developers.

In Node.js, processing form data is a very common operation, and the drop-down box is a common form element. Drop-down boxes are generally used to provide multiple options, and users can select one of the options to achieve a specific function. In some scenarios, we need to set the default value of the drop-down box. Let's introduce how to set the default value of the drop-down box in Node.js.

You need to use a third-party module to process form data in Node.js - body-parser.

First, we install the body-parser module in the terminal:

$ npm install body-parser

Then, introduce the module in the code:

const express = require('express')
const bodyParser = require('body-parser')
const app = express()

Next, use body-parserThe urlencoded method of the module performs form data parsing:

app.use(bodyParser.urlencoded({ extended: false }))

In the front-end page, we need to define the drop-down box through HTML code and give a default value . As shown below:

<select name="fruit">
  <option value="apple">Apple</option>
  <option value="banana">Banana</option>
  <option value="orange" selected>Orange</option>
</select>

In the selection box, we set the default option to the selected state.

Finally, in the callback function that processes form data in Node.js, we can obtain the form data through req.body, and then obtain the value of the drop-down box. If no option is selected in the form, we can set the default value to that option in the selected status. As shown below:

app.post('/submit', (req, res) => {
  const { fruit } = req.body
  if (!fruit) {
    document.querySelector('select option[value=orange]').setAttribute('selected', true)
  }
  // ...
})

The above is how to set the default value of the drop-down box in Node.js. It should be noted that in the front-end page, we need to add the selected attribute to the default option, and in the Node.js callback function, we need to make corresponding judgments to set the default value. In this way, we can flexibly set the default value of the drop-down box, making the user experience smoother.

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