Making an add 'empty column' button [JAVASCRIPT]

Hello,

I'm trying to make multiple buttons that when hit will pull the fields above It down until it hits the field where the button lies:

 Once all the fields move down then the value of the fields that are next to the button pressed will be changed to "".

I have tried to use the following code but it does not seem to work:

  var idNumber = parseInt(event.target.name.replace("Add", ""));
for (var i = 40; i >= idNumber; i--) {
    this.getField("ID" + i).value = this.getField("ID" + (i - 1)).value;
    this.getField("Desc" + i).value = this.getField("Desc" + (i - 1)).value;
    this.getField("No" + i).value = this.getField("No" + (i - 1)).value;
    this.getField("Unit" + i).value = this.getField("Unit" + (i - 1)).value;
    this.getField("Price" + i).value = this.getField("Price" + (i - 1)).value;
    this.getField("Total" + i).value = this.getField("Total" + (i - 1)).value;
}
    this.getField("ID" + idNumber).value = "";
    this.getField("Desc" + idNumber).value = "";
    this.getField("No" + idNumber).value = "";
    this.getField("Unit" + idNumber).value = "";
    this.getField("Price" + idNumber).value = "";
    this.getField("Total" + idNumber).value ="";

This code just replicates the first field that has a value to the fields under it one time.

Can someone please help me with this problem?

Thank you.