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March 10, 2025 22:22
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DOM Selection API Cheatsheet

A quick reference guide to the HTML DOM Selection API, covering essential methods, properties, and event handling for managing text selections in web applications.

Selection Basics

Obtaining the Selection Object

Use document.getSelection() to retrieve the Selection object representing the range of text selected by the user or the current position of the caret.

var selection = document.getSelection();

Selection Object Properties

selection.anchorNode

The node in which the selection begins.

selection.anchorOffset

The offset into the anchorNode at which the selection begins.

selection.focusNode

The node in which the selection ends.

selection.focusOffset

The offset into the focusNode at which the selection ends.

selection.isCollapsed

A boolean indicating whether the selection’s start and end points are at the same position.

selection.rangeCount

The number of ranges in the selection.

Example 

<p id="myText">This is some text.</p>
<button onclick="getSelectionInfo()">Get Selection Info</button>

<script>
function getSelectionInfo() {
  var sel = document.getSelection();
  console.log('Anchor Node:', sel.anchorNode);
  console.log('Anchor Offset:', sel.anchorOffset);
  console.log('Focus Node:', sel.focusNode);
  console.log('Focus Offset:', sel.focusOffset);
  console.log('Is Collapsed:', sel.isCollapsed);
}
</script>

Manipulating Selections

Adding and Removing Ranges

selection.addRange(range)

Adds a Range object to the selection.

selection.removeRange(range)

Removes a Range object from the selection.

selection.removeAllRanges()

Removes all ranges from the selection, effectively deselecting everything.

Creating and Using Ranges 

var range = document.createRange();
range.setStart(startNode, startOffset);
range.setEnd(endNode, endOffset);

selection.addRange(range);

Example: Selecting part of a text node.

<p id="textContainer">Hello, world!</p>
<button onclick="selectText()">Select 'world'</button>

<script>
function selectText() {
  var textContainer = document.getElementById('textContainer');
  var range = document.createRange();
  range.setStart(textContainer.firstChild, 7);
  range.setEnd(textContainer.firstChild, 12);

  var selection = document.getSelection();
  selection.removeAllRanges();
  selection.addRange(range);
}
</script>

Selection State Manipulation

Collapsing Selections

selection.collapse(node, offset)

Collapses the selection to a single point at the specified node and offset.

selection.collapseToStart()

Collapses the selection to its start point.

selection.collapseToEnd()

Collapses the selection to its end point.

Checking Node Containment

selection.containsNode(node, partlyContained) - Indicates if the specified node is part of the selection.

  • node: The node to check.
  • partlyContained (optional): A boolean. If true, the method returns true if part of the node is contained in the selection. If false (default), only returns true if the entire node is contained in the selection.
var isContained = selection.containsNode(element, true);

Advanced Selection Techniques

Deleting Content from the Document

selection.deleteFromDocument() - Deletes the selected content from the document.

selection.deleteFromDocument();

Example: Delete selected text when a button is clicked.

<p id="deletableText">Select this text and click delete.</p>
<button onclick="deleteSelected()">Delete Selection</button>

<script>
function deleteSelected() {
  var selection = document.getSelection();
  selection.deleteFromDocument();
}
</script>

Listening for Selection Changes

Use the selectionchange event to monitor changes to the document’s selection.

document.addEventListener('selectionchange', () => {
  console.log('Selection changed');
  var selection = document.getSelection();
  console.log('Selected text:', selection.toString());
});