How to implement form autofill function in JavaScript?

How to implement form autofill function in JavaScript?

In actual development, we often encounter the need for automatic filling of forms. For example, after a user enters their username on the login page, they want the corresponding password to be automatically filled in. This can improve the user experience and reduce repeated input.

JavaScript provides a simple and effective way to implement form autofill functionality. Below we will introduce in detail how to use JavaScript to implement this function and provide corresponding code examples.

First, we need to define a form in HTML and set the corresponding id attribute for the input box that needs to be automatically filled. For example, we have a login form with two input boxes for username and password. We set the ids for them to "username" and "password" respectively.

<form>
  <label for="username">用户名：</label>
  <input type="text" id="username" name="username" required>

  <label for="password">密码：</label>
  <input type="password" id="password" name="password" required>

  <input type="submit" value="登录">
</form>

Next, we need to use JavaScript to implement the autofill function. We can get the value of the input box and then fill it into another input box.

window.onload = function() {
  var usernameInput = document.getElementById("username");
  var passwordInput = document.getElementById("password");

  usernameInput.addEventListener("input", function() {
    passwordInput.value = this.value;
  });
};

In the above code, we added an input event listener to the user name input box through the addEventListener method. This event is triggered when the user enters content in the input box. In the event callback function, we obtain the value of the username input box through this.value and assign it to the value attribute of the password input box.

In this way, when the user enters content in the username input box, the password input box will automatically fill in the same content.

It should be noted that the above code is just a simple example, and the actual form autofill function may be more complex. For example, we may need to determine whether to autofill based on certain conditions. Additionally, to ensure security, we should avoid autofilling sensitive information such as passwords.

To summarize, using JavaScript to implement the form auto-fill function can improve the user experience and reduce repeated input by users. We can fill in the content in the corresponding input box by listening to the events of the input box. Of course, the specific implementation will vary according to actual needs.

I hope the above introduction will help you understand how to use JavaScript to implement the form auto-fill function. If you have other questions or needs, you can also use JavaScript to solve them in a similar way.

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