Use the required attribute of HTML to verify the required items in the form. The basic usage is to add this attribute to the input, textarea or select element to ensure that the user can only allow submission after filling it out; 1. Support common input types such as text, email, password, number, date, textarea and select; 2. For radio buttons, you need to add required for the radio name to ensure that at least one is selected; 3. At least one must be selected after adding required to the multi-check box; 4. The default value of the select element cannot be an empty string, otherwise it will be considered unselected; mainstream browsers support required, but old versions may be incompatible, so you need to cooperate with JS verification at this time; the prompt content can be customized through the setCustomValidity() method to improve the user experience; although required is simple and effective, complex verification such as password strength, consistency of two inputs, or remote verification still requires JavaScript or backend support.
Verify the required items when submitting the form. required attribute of HTML is indeed a simple and practical method. It can directly check whether the user has missed filling on the browser side, so as to save the backend verification after the form is submitted.
Basic usage of required attribute
In HTML forms, just add required attributes to form controls such as input, select, or textarea, and the browser will automatically check whether these fields have been filled in when submitting.
for example:
<input type="text" name="username" required>
In this way, if the user submits the form without filling in the user name, the browser will pop up a prompt to prevent the submission. Basic verification is achieved without writing a line of JavaScript.
Supported form element types
Not all form elements can be required , but several common types support:
-
<input>(including text, email, password, number, date, etc.) -
<textarea> -
<select>
A few points to note:
- To ensure that at least one of the radio buttons is selected, generally
requiredis added to all radios of the same name. - After multiple selection (checkbox) plus
required, choose at least one. - For
<select>, the default value cannot be an empty string, otherwiserequiredwill be considered unselected.
For example:
<label>Select your favorite fruit:</label> <select name="fruit" required> <option value="">--Please choose an option--</option> <option value="apple">Apple</option> <option value="banana">Banana</option> </select>
If the user does not select any valid items, it will be prompted when submitting.
Browser compatibility and style control
Now mainstream browsers support required , including Chrome, Firefox, Safari and Edge. However, some old versions may not be recognized, so if you need better compatibility, you still need to cooperate with JS verification.
In addition, the default prompt message style of the browser is ugly, and it cannot be modified directly with CSS. But you can customize the prompt content through setCustomValidity() method:
<input type="email" name="email" required oninvalid="this.setCustomValidity('Please enter a valid email address')">
Of course, this requires a little bit of JS support, but it can improve the user experience.
Use required or JavaScript?
The answer is: It can be used together.
required is the first line of defense for front-end verification, simple and effective. But if you need more complex logic, such as verifying the password strength, confirming the two inputs are consistent, remotely verifying whether the username exists, etc., you have to use JavaScript or backend verification.
To summarize:
-
requiredis a basic but effective form verification method - It works with most common input types
- More complex control can be done in combination with JS
- Don't rely entirely on it for all verification
Basically that's it. If required is used properly, it can save a lot of trouble.
The above is the detailed content of HTML `required` Attribute for Form Validation. For more information, please follow other related articles on the PHP Chinese website!
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