How does the required attribute work for form validation?
Jun 28, 2025 am 01:56 AMThe required property is used to set the form field to be required, and the user cannot submit it if it has not filled in. 1. Add required attributes to HTML, without JavaScript; 2. It is often used with input types such as text, email, number, checkbox, radio, etc.; 3. The default prompt information of the browser cannot be customized, and JavaScript must be matched when a unified prompt is required; 4. Situations that may not work include: the formnovalidate attribute of the submission button, the input box is disabled, the label structure is incorrect, or browser compatibility issues.
The required
property in form verification is actually very simple. It tells the browser that the input box cannot be empty. If the user fails to fill in, the browser will automatically prompt "Please fill in this field". No JavaScript is required, pure HTML can handle basic verification.
1. Basic usage of required
attribute
Adding the required
attribute to the HTML form element can make this field a required item. for example:
<input type="text" name="username" required>
Or more commonly, use it with labels:
<label for="email">Email:</label> <input type="email" id="email" name="email" required>
As long as this attribute is added, the user must fill in the content before submitting the form. Note: required
is a Boolean property, no value is required, and it will take effect after writing.
2. Common input types used for combinations
Although required
is universal, it works better with certain types of inputs, such as:
-
type="text"
(normal text) -
type="email"
(email format) -
type="number"
(number) -
type="checkbox"
(checkbox) -
type="radio"
(radio button)
For example, if you want the user to have to choose a gender:
<input type="radio" name="gender" value="male" required> Male<input type="radio" name="gender" value="female"> Female
In this way, the user has to choose at least one to pass the verification.
3. The prompt message cannot be customized
By default, the browser will pop up a prompt when the user submits without filling in it. The copywriting displayed by different browsers may be different. For example, Chrome shows "Please fill in this field", while Firefox may say "This field cannot be empty".
?? Note: If you need a unified prompt or want to beautify the prompt box, you cannot rely solely on required
, but you have to cooperate with JavaScript to do custom verification.
4. In some cases, required
does not work
Sometimes you will find required
is like failure, which may be due to the following reasons:
- The form uses the
formnovalidate
attribute submission button, and verification will be skipped; - The input box is disabled (
disabled
), and the browser will not verify; - The wrong label structure was used, such as not correctly associated with
label
andinput
; - Compatibility is poor in some older mobile browsers.
Therefore, it is best to test the code after writing it to ensure that verification can be triggered normally in various situations.
Basically that's it. Although the function is simple, it can save a lot of trouble if used correctly.
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