Function isNumeric

isNumeric(text?: null | string): boolean
Returns whether all the characters in the given text is numeric
Parameters
- Optionaltext: null | string
  the text to check
Returns boolean
whether all the characters in the given text is numeric
Author
David Hsing
Example
```
isNumeric(undefined);    // false
isNumeric('abc123');    // false
isNumeric('123456');    // true
```