Function prependIfMissing

prependIfMissing(text?, prefix?): string | undefined | null
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 string | undefined | null
a string that concat the given prefix and text
Example
```
prependIfMissing('bar', 'foo');    // 'foobar'
prependIfMissing('foobar', 'foo');    // 'foobar'
```