HTMLTableSectionElement: insertRow() method
  The insertRow() method of the HTMLTableSectionElement interface inserts a new row
  (<tr>) in the given table sectioning element (<thead>, <tfoot>, or
  <tbody>), then returns a reference to this new row.
    Note: insertRow() inserts the row directly into the
    section. The row does not need to be appended separately as would be the case if
    Document.createElement() had been used to create the new
    <tr> element.
  
Syntax
insertRow()
insertRow(index)
Parameters
- indexOptional
- 
    The row index of the new row. If indexis-1or equal to the number of rows, the row is appended as the last row. Ifindexis omitted it defaults to-1.
Return value
An HTMLTableRowElement that references the new row.
Exceptions
- IndexSizeError- DOMException
- 
    Thrown if indexis greater than the number of rows, or smaller than-1.
Examples
In this example, two buttons allow you to add and remove rows from the table body section; it also updates a <output> element with the number of rows currently in the table.
HTML
<table>
  <thead>
    <th>Col 1</th>
    <th>Col 2</th>
    <th>Col 3</th>
  </thead>
  <tbody>
    <tr>
      <td>X</td>
      <td>Y</td>
      <td>Z</td>
    </tr>
  </tbody>
</table>
<button id="add">Add a row</button>
<button id="remove">Remove last row</button>
<div>This table's body has <output>1</output> row(s).</div>
Javascript
// Obtain relevant interface elements
const bodySection = document.querySelectorAll("tbody")[0];
const rows = bodySection.rows; // The collection is live, therefore always up-to-date
const rowNumberDisplay = document.querySelectorAll("output")[0];
const addButton = document.getElementById("add");
const removeButton = document.getElementById("remove");
function updateRowNumber() {
  rowNumberDisplay.textContent = rows.length;
}
addButton.addEventListener("click", () => {
  // Add a new row at the end of the body
  const newRow = bodySection.insertRow();
  // Add cells inside the new row
  ["A", "B", "C"].forEach(
    (elt) => (newRow.insertCell().textContent = `${elt}${rows.length}`),
  );
  // Update the row counter
  updateRowNumber();
});
removeButton.addEventListener("click", () => {
  // Delete the row from the body
  bodySection.deleteRow(-1);
  // Update the row counter
  updateRowNumber();
});
Result
Specifications
| Specification | 
|---|
| HTML Standard # dom-tbody-insertrow | 
Browser compatibility
BCD tables only load in the browser