typeof cell smart table always string

I putted some condition for columns like for example the input must be a number for example:
```
onCreateConfirm(event): void {
var data = { cost : event.newdata.cost}
if( typeof data.cost !== "number") { window.confirm("enter a number please") else { ..do thnigs..}
}
```
The problem here is any data that i enter is always evaluated as type strings even dates.