Text.splitText()

The splitText() method of the Text interface breaks the Text node into two nodes at the specified offset, keeping both nodes in the tree as siblings.

After the split, the current node contains all the content up to the specified offset point, and a newly created node of the same type contains the remaining text. The newly created node is returned to the caller. If the original node had a parent, the new node is inserted as the next sibling of the original node. If the offset is equal to the length of the original node, the newly created node has no data.

Separated text nodes can be concatenated using the Node.normalize() method.

newNode = textNode.splitText(offset)

<p>foobar</p>

const p = document.querySelector('p');

// Get contents of <p> as a text node
const foobar = p.firstChild;

// Split 'foobar' into two text nodes, 'foo' and 'bar',
// and save 'bar' as a const
const bar = foobar.splitText(3);

// Create a <u> element containing ' new content '
const u = document.createElement('u');
u.appendChild(document.createTextNode(' new content '));

// Add <u> before 'bar'
p.insertBefore(u, bar);

// The result is: <p>foo<u> new content </u>bar</p>