Function substringBefore

substringBefore(text?, separator?): string | undefined
Returns the substring before the first occurrence of the given separator (the separator is not returned)
Parameters
- Optionaltext: null | string
  the string to get a substring from
- Optionalseparator: null | string
  the String to search for
Returns string | undefined
the substring before the first occurrence of the given separator
Example
```
substringBefore("foo/bar/foo/bar", "/");    // 'foo'
```