selectstart

Selectstart refers to a browser event that fires when a user begins selecting text within a document. The concept originated in Internet Explorer as the onselectstart event, and various engines historically offered similar behavior to control text selection. In modern browsers, support for selectstart is uneven, and its implementation can vary or be absent. The event is cancelable, meaning a handler can prevent the default text-selection action by calling preventDefault.

Common usage involves attaching a listener to the element (or to the document) to intercept the start of a selection. For example, a handler that calls e.preventDefault() will stop the browser from selecting text on that element. Because of inconsistent support across browsers, relying on selectstart for cross-browser behavior is generally discouraged in favor of more standard approaches.

For broader cross-browser control of text selection, developers typically use CSS. The property user-select (with vendor-prefixed variants such as -webkit-user-select and -moz-user-select) allows preventing user selection on an element with the value none. This method is generally more reliable and consistent than bindable event handling. It is important to note that disabling text selection does not provide security or rights protection for content; users can still access content through other means, so such techniques should be used for UX considerations rather than protection.

Related concepts include the selectionchange event, which fires when the document's selection changes, and dragstart, which governs dragging behavior of content. Selectstart remains a historical and partly supported mechanism, with CSS-based approaches preferred for modern web development.