Function flatMap

flatMap is a essentially a combination of the map operator followed by flatten. The mapping function can be any function that produces an iterable:

• that means it could be an array
• but it can also be a generator function that can yield 0, 1 or more values
• and it could also be a ReadableStream
• and it could be the result of another pipe chain of operators

All elemants will be handled, and there is no state held between the values of the input operator.

Example

 // output an array with double the values of the input array
 pipe(
   itr8FromArray([1, 2, 3]),
   flatMap((n) => [n, n * 2]),
 );  // => 1, 2, 2, 4, 3, 6

 // categorize by divisibility by 2, 3, 5, 7 by using a generator function
 pipe(
   itr8Range(1, 16),
   flatMap(function* (n) => {
     if (n % 2 === 0) yield [2, n];
     if (n % 3 === 0) yield [3, n];
     if (n % 5 === 0) yield [5, n];
     if (n % 7 === 0) yield [7, n];
   }),
 ); // => [2, 2], [3, 3], [2, 4], [5, 5], [2, 6], [3, 6], [2, 8], [7, 7], [2, 10], [5, 10], [2, 12], [3, 12], [2, 14], [7, 14], [3, 15], [5, 15], [2, 16]

 // categorize by divisibility by 2, 3, 5, 7 by using another itr8 chain
 pipe(
   itr8Range(1, 16),
   flatMap((n) => pipe(
     itr8FromSingleValue(n),
     map((n) => {
       let result = [];
       if (n % 2 === 0) result.push([2, n]);
       if (n % 3 === 0) result.push([3, n]);
       if (n % 5 === 0) result.push([5, n]);
       if (n % 7 === 0) result.push([7, n]);
     }),
   ),
 ),

Returns