Range: selectNodeContents() method

selectNodeContents(referenceNode)

const range = document.createRange();
const referenceNode = document.querySelector("div");
range.selectNodeContents(referenceNode);

<p id="p">
  <strong>Use the buttons below</strong> to select or deselect the contents of
  this paragraph.
</p>
<button id="select-button">Select paragraph</button>
<button id="deselect-button">Deselect paragraph</button>

const p = document.getElementById("p");
const selectButton = document.getElementById("select-button");
const deselectButton = document.getElementById("deselect-button");
selectButton.addEventListener("click", (e) => {
  // Clear any current selection
  const selection = window.getSelection();
  selection.removeAllRanges();
  // Select paragraph
  const range = document.createRange();
  range.selectNodeContents(p);
  selection.addRange(range);
});
deselectButton.addEventListener("click", (e) => {
  const selection = window.getSelection();
  selection.removeAllRanges();
});