There are a number of isNaN(value) tests lurking around. If we want to explicitly check if a string represents a number, I'd like to add a OpenLayers.String.isNumeric function.
Comparisons (assuming you think !isNaN is a good test to see if a string is numeric):
Areas of agreement
!isNaN("foo") // false
OpenLayers.String.isNumeric("foo") // false
!isNaN("1") // true
OpenLayers.String.isNumeric("1") // true
!isNaN(undefined) // false
OpenLayers.String.isNumeric(undefined) // false
Areas of disagreement
!isNaN("") // true
OpenLayers.String.isNumeric("") // false
!isNaN(null) // true
OpenLayers.String.isNumeric(null) // false
!isNaN(true) // true
OpenLayers.String.isNumeric(true) // false
!isNaN(false) // true
OpenLayers.String.isNumeric(false) // false
