Function isAlphanumeric

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