Mastering
HTML maxlength Attribute

Understanding What is the maxlength Attribute?

The maxlength attribute in HTML specifies the maximum number of characters (in UTF-16 code units) a user can enter into an or </code> element. This attribute is crucial for controlling input length and ensuring data integrity.</p><p class="text-neutral-700 leading-relaxed mb-6 text-lg ">The value of <code>maxlength</code> must be a non-negative integer. If not specified or set to an invalid value, the input field has no maximum length restriction. The count is based on UTF-16 code units which generally equates to the number of characters but is not always a one-to-one mapping.</p></section><section data-section-id="usage-and-syntax"><h2 id="usage-and-syntax" class="text-3xl lg:text-4xl font-bold text-primary mb-8 leading-tight"><span class="bg-gradient-to-r from-indigo-500 via-purple-500 to-pink-500 bg-clip-text text-transparent">Usage</span> <!-- -->How to Use maxlength in HTML Forms</h2><p class="text-neutral-700 leading-relaxed mb-6 text-lg font-medium">To use the <code>maxlength</code> attribute, simply add it to your <code><input></code> or <code><textarea></code> tag, followed by the desired maximum length:</p><p class="text-neutral-700 leading-relaxed mb-6 text-lg "><code>`</code>html <input type="text" id="username" name="username" maxlength="20"> <textarea id="comments" name="comments" maxlength="500"> `

In this example, the username input field will allow a maximum of 20 characters, and the comments textarea is limited to 500 characters.

Constraint maxlength and Validation

The maxlength attribute plays a role in HTML5 form validation. If a user enters text exceeding the specified maxlength, the input will fail constraint validation. However, browser behavior can vary, some will prevent the user from entering too many characters, others will allow it and trigger validation errors.

Constraint validation is only triggered when the input's value is modified by the user. Read-only properties of the element's object will also update if the length goes beyond the permitted value.

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The maxlength attribute is a key element in building user-friendly and data-secure HTML forms.

MDN Contributors (Modified)

Best Practices for maxlength

Always set appropriate maxlength values based on the expected input. Consider the type of data and its intended use.

Use maxlength in conjunction with other validation techniques (e.g., client-side and server-side validation) for comprehensive input control.

Provide clear feedback to users if their input exceeds the allowed length, such as an error message or a character counter.