index.md

---

title: id
slug: Web/HTML/Global_attributes/id
page-type: html-attribute
browser-compat: html.global_attributes.id

---

{{HTMLSidebar("Global_attributes")}}

The id global attribute defines an identifier (ID) which must be unique in the whole document. Its purpose is to identify the element when linking (using a fragment identifier), scripting, or styling (with {{glossary("CSS")}}).

{{EmbedInteractiveExample("pages/tabbed/attribute-id.html","tabbed-shorter")}}

Warning: This attribute's value is an opaque string: this means that web authors should not rely on it to convey human-readable information (although having your IDs somewhat human-readable can be useful for code comprehension, e.g. consider ticket-18659 versus r45tgfe-freds&$@).

id's value must not contain {{glossary("whitespace")}} (spaces, tabs etc.). Browsers treat non-conforming IDs that contain whitespace as if the whitespace is part of the ID. In contrast to the {{htmlattrxref("class")}} attribute, which allows space-separated values, elements can only have one single ID value.

Note: Technically, the value for an id attribute may contain any character, except {{glossary("whitespace")}} characters. However, to avoid inadvertent errors, only {{glossary("ASCII")}} letters, digits, '_', and '-' should be used and the value for an id attribute should start with a letter. For example, . has a special meaning in CSS (it acts as a class selector). Unless you are careful to escape it in the CSS, it won't be recognized as part of the value of an id attribute. It is easy to forget to do this, resulting in bugs in your code that could be hard to detect.

Specifications

{{Specifications}}

Browser compatibility

{{Compat}}

See also

• All global attributes.

• {{domxref("Element.id")}} that reflects this attribute.

• The {{domxref("Document.getElementById")}} method.

• CSS ID selectors.