Array.prototype.flatMap()
Array.prototype.flatMap() is a JavaScript method in the Array category. Maps each element then flattens the result one level. The syntax is array.flatMap(callbackFn). A typical example: [1, 2, 3].flatMap(x => [x, x * 2]) // [1, 2, 2, 4, 3, 6]. Its time complexity is O(n), which matters when it runs over large inputs. A close sibling is Array.prototype.map(), which creates a new array populated with the results of calling a provided function on every element. A close sibling is Array.prototype.filter(), which creates a new array with all elements that pass the test implemented by the provided function. A close sibling is Array.prototype.reduce(), which executes a reducer function on each element, resulting in a single output value. A close sibling is Array.prototype.forEach(), which executes a provided function once for each array element. More about this category: Array methods for manipulating arrays — map, filter, reduce, find, and more.