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  4. HTML attribute: maxlength

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草案
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maxlength attribute defines the maximum number of characters (as UTF-16 code units) the user can enter into an <input> or <textarea> . This must be an integer value 0 or higher. If no maxlength is specified, or an invalid value is specified, the input or textarea has no maximum length.

任何 maxlength value must be greater than or equal to the value of minlength , if present and valid. The input will fail constraint validation if the length of the text value of the field is greater than maxlength UTF-16 code units long. Constraint validation is only applied when the value is changed by the user.

Constraint validation

While the browser will generally prevent user from entering more text than the maxlength attribute allows, should the length be longer than the maxlength allows, the read-only tooLong property of a ValidityState object will be true.

范例 

<input type="password" maxlength="4"/>

规范

规范 状态
HTML 实时标准
The definition of 'maxlength attribute' in that specification. 		实时标准
HTML 5.1
The definition of 'maxlength attribute' in that specification. 		推荐

浏览器兼容性

The compatibility table on this page is generated from structured data. If you'd like to contribute to the data, please check out https://github.com/mdn/browser-compat-data and send us a pull request.

No compatibility data found. Please contribute data for "html.elements.attribute.maxlength" (depth: 1) to the MDN 兼容性数据存储库 .

另请参阅

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