setColumnDefs is not working for some ag-grids

I have several ag-grids in my code and the "setColumnDefs" is working for all the grids, however when I am trying to create a new grid, I am getting the error: Cannot read property 'setColumnDefs' of undefined. I don't know what I'm doing wrong. It seems to work for other ag-grids.

vm.newGrid = {
            enableSorting: true,
            enableColResize: true
        };

var newGridColumns = [
            {
                headerName: 'DATA',
                field: 'data',
            }, {
                headerName: 'PERCENT',
                field: 'percent'
            }
        ];

vm.newGrid.api.setColumnDefs(newGridColumns);