spreadMap

It works like the map() method, but one value is mapped to more values. It is achieved by returning an array of values to spread into the final array from a callback passed to the method.

spreadMap(
 (item, index, array) => array
)

As of ES10 you can use built-in flatMap() method instead.

Example

const arr = [1,2,3,4];
const sm = arr.spreadMap(
  x => [x, x**2]
);

console.log(sm);
// [1,1,2,4,3,9,4,16]