Validation API

Validation API （验证API）

Validation API: Client-Side Form Validation in Web Applications #

Validation API: Client-Side Form Validation in Web Applications

The Validation API is a web technology that empowers web developers to perform client-side form validation, ensuring that user input meets specific criteria before it is submitted to a server. It provides a convenient way to enhance user experience by offering real-time feedback on form input errors, reducing the likelihood of incorrect data being sent to the server. In this article, we’ll explore what the Validation API is, its benefits, how it works, and how to use it effectively in web development.

What is the Validation API? #

The Validation API is a JavaScript API that allows developers to define and enforce validation rules for form elements in web applications. It offers a set of attributes, methods, and properties that can be used to specify constraints on form fields, such as required fields, minimum and maximum input lengths, and patterns for valid input. （验证API是一个JavaScript API ，允许开发人员定义和实施Web应用程序中表单元素的验证规则。它提供了一组属性、方法和属性，可用于指定表单字段的约束，例如必填字段、最小和最大输入长度以及有效输入的模式。）

Benefits of the Validation API #

Improved User Experience The Validation API enhances the user experience by providing real-time feedback to users as they fill out forms. It alerts them to errors immediately, reducing frustration and the likelihood of submitting incorrect data. Reduced Server Load By validating user input on the client side, the Validation API can help reduce unnecessary form submissions to the server, saving server resources and bandwidth. Faster Error Identification Users can quickly identify and correct errors before submitting a form, resulting in more accurate and complete data being sent to the server. Custom Validation Logic Developers can implement custom validation logic using JavaScript to enforce complex validation rules that are specific to their application.

How the Validation API Works #

The Validation API operates primarily through HTML attributes that are added to form elements. These attributes define various validation constraints. Some of the key attributes include:

• ‘required’: Indicates that a field must be filled out before submitting the form.

• ‘maxlength’ and ‘minlength’: Specifies the maximum and minimum length of text input, respectively.

• ‘pattern’: Defines a regular expression pattern that the input value must match.

• ’type’ attribute: Depending on the input type (e.g., ’email’, ’number’, ‘url’), specific validation rules are applied.

In addition to these attributes, developers can use JavaScript to access and manipulate form elements and their validation states. For example, the ‘checkValidity()’ method can be used to trigger validation checks programmatically, and the ‘setCustomValidity()’ method allows developers to set custom error messages. （除了这些属性外，开发人员还可以使用JavaScript来访问和操作表单元素及其验证状态。例如， “checkValidity ()”方法可用于以编程方式触发验证检查，而“setCustomValidity ()”方法允许开发人员设置自定义错误消息。）

Using the Validation API #

Here’s a basic example of how to use the Validation API to perform client-side validation on a form input field:

<form>
 <label for="email">Email:</label>
 <input type="email" id="email" name="email" required>
 <button type="submit">Submit</button>
</form>

In this example:

• We have an input field with type=“email” and the required attribute, indicating that it must be filled out before submission. （-我们有一个type = “email"和必填属性的输入字段，表明必须在提交前填写。）

• The browser will automatically validate the input against the email format, ensuring that it contains a valid email address. （-浏览器将根据电子邮件格式自动验证输入，确保其包含有效的电子邮件地址。）

• If the user attempts to submit the form without entering a valid email address, the browser will display an error message, preventing submission until the input is valid. （-如果用户尝试在未输入有效电子邮件地址的情况下提交表单，浏览器将显示错误消息，在输入有效之前无法提交。）

// JavaScript code to access the form element
const form = document.querySelector('form');

// Adding a submit event listener to the form
form.addEventListener('submit', (event) => {
 if (!form.checkValidity()) {
   // Prevent form submission if validation fails
（//如果验证失败，则阻止表单提交）
   event.preventDefault();
   alert('Please fill out the form correctly.');
 }
});

In this JavaScript code:

• We select the form element using document.querySelector(). （-我们使用document.querySelector ()选择表单元素。）

• We add a submit event listener to the form. （-我们在表单中添加了一个提交事件监听器。）

• Inside the event listener, we use form.checkValidity() to check if the form input is valid. If validation fails, we prevent the form from being submitted and display an alert to the user. （-在事件侦听器中，我们使用form.checkValidity ()来检查表单输入是否有效。如果验证失败，我们将阻止提交表单，并向用户显示警报。）

By utilizing the Validation API, web developers can ensure that user input is accurate and complete, leading to a smoother user experience and reducing the likelihood of data errors in web applications. （通过使用验证API ， Web开发人员可以确保用户输入的准确性和完整性，从而实现更流畅的用户体验，并降低Web应用程序中出现数据错误的可能性。）