C# - Javascript Undefined Attribute - Why Source.full Is Always Undefined On The First Click

I have a GridView with the following event:

protected void GridView1_RowCreated(object sender, GridViewRowEventArgs e)
{
foreach (TableCell c in e.Row.Cells)
{
c.Attributes.Add("full","false");
}
}

And in my javascript I have an onClick event for every cell:

if(source.full="false")
{
...
source.full="true";
}
else
{
...
source.full="false";
}

Why is it that source.full is always undefined on the first click?