Insert a Row

[admin]

How do I insert a row before a given row....I have written the following code but doesn't seem to work -

var myTable = document.getElementById("Matrix");
var myNewRow = document.createElement("TR");
var prevRow = document.getElementById("r2");

myTable.insertBefore(myNewRow,prevRow);
myNewRow.innerText = "NewRow";
myNewRow.id = abc;