To set whether a table border is to be collapsed, use the borderCollapse property and set it to collapse. You can try to run the following code to set the table border to collapse −
Example
<!DOCTYPE html>
<html>
<body>
<table id="newTable" border="2">
<tr>
<th>EmpID</th>
<th>EmpName</th>
<th>EmpDept</th>
</tr>
<tr>
<td>001</td>
<td>Amit</td>
<td>IT</td>
</tr>
<tr>
<td>002</td>
<td>John</td>
<td>Finance</td>
</tr>
<tr>
<td>003</td>
<td>David</td>
<td>Marketing</td>
</tr>
</table>
<br>
<button onclick="display()">Click to collapse</button>
<script>
function display() {
document.getElementById("newTable").style.borderCollapse = "collapse";
}
</script>
</body>
</html>