Returns true if searchString appears as a substring of the result of converting this
object to a String, at one or more positions that are
greater than or equal to position; otherwise, returns false.
Parameters
searchString: string
search string
Optionalposition: number
If position is undefined, 0 is assumed, so as to search all of the String.
Returns true if searchString appears as a substring of the result of converting this object to a String, at one or more positions that are greater than or equal to position; otherwise, returns false.