Function prependIfMissing

prependIfMissing(
text?: null | string,
prefix?: string,
): undefined | null | string
Returns a string that concat the given prefix and text
Parameters
- Optionaltext: null | string
  the text to check
- Optionalprefix: string
  the prefix to prepend
Returns undefined | null | string
a string that concat the given prefix and text
Author
David Hsing
Example
```
prependIfMissing('bar', 'foo');    // 'foobar'
prependIfMissing('foobar', 'foo');    // 'foobar'
```