elemOfStr ()

elemOfStr(haystack): ((needle) => boolean)
Checks if a substring is in a string.
Parameters
- haystack: string
  The string to search in
Returns ((needle) => boolean)
A function that takes a needle (substring) and returns true if it's in the haystack
- - (needle): boolean
  - Parameters
    - needle: string
    Returns boolean
Example
```
elemOfStr('abc')('a') // true
elemOfStr('abc')('ab') // true
elemOfStr('abc')('d') // false
opt('ab').exists(elemOfStr('abc')) // true
```
See
- Opt.elemOfStrIn
- elemOfStrIn
- Defined in Opt.ts:2542