Browser.ExecJS("eval('" & yourString & "');")
I think that will return a string with the evaluated value. And then you can do:
Browser.ExecJS("!isNaN(""" & value & """);")=1?float(value)%1<>0?float(value):int(value):value
which will give you it as either a float,int,or string if it isn't NaN.