Range: setStart() メソッド

setStart(startNode, startOffset)

<p id="address">
  Wyatt Earp<br />
  101 E. Main St.<br />
  Dodge City, KS<br />
  67801<br />
  USA
</p>

<hr />
<p>Nodes in the original address:</p>
<ol id="log"></ol>

const address = document.getElementById("address");
const log = document.getElementById("log");

// Log info
address.childNodes.forEach((node) => {
  const li = document.createElement("li");
  li.textContent = `${node.nodeName}, ${node.nodeValue}`;
  log.appendChild(li);
});

// Highlight the street and city
const startOffset = 2; // Start at third node: 101 E. Main St.
const endOffset = 5; // End at fifth node: Dodge City, KS
const range = document.createRange();
range.setStart(address, startOffset);
range.setEnd(address, endOffset);

const mark = document.createElement("mark");
range.surroundContents(mark);

<p id="content">0123456789</p>
<p id="log"></p>

const element = document.getElementById("content");
const textNode = element.childNodes[0];
const range = document.createRange();
range.setStart(textNode, 0); // Start at first character
range.setEnd(textNode, 5); // End at fifth character
document.getElementById("log").textContent = range;