proper way to pass variable to a js function in column

i note that whilst this works under columns, returning the value of myvar
{ data: null, render: function (data, type, row, meta){return data.myvar}}
which is equivalent to
{ data: 'myvar' }

this doesn't and returns a null
{ data: null, render: function (data, type, row, meta){return data.myvar.replace(/[,]+/g, " ")}}

what's the proper way to pass the myvar variable to a js function?