The flat() method creates a new array with all sub-array elements concatenated into it recursively up to the specified depth.
Syntax:
const newArray = arr.flat([depth]);Example:
const nestedValues = [1, [2, 3], [ [] ], [4, [5]], 6 ]];
nestedValues.flat(0); //[1, [2, 3], [ [] ], [4, [5]], 6 ]]
nestedValues.flat(/* default: 1 */); //[1, 2, 3, [] , 4, [5], 6 ]
nestedValues.flat(2); //[1, 2, 3 , 4, 5, 6 ]The flatMap() method first maps each element using a mapping function, then flattens the result into a new array. It is identical to a map followed by a flat of depth 1, but flatMap is often quite useful, as merging both into one method is slightly more efficient.
Syntax:
var new_array = arr.flatMap(function callback(currentValue[, index[, array]]) {
// return element for new_array
}[, thisArg])Example:
[1,2,3].map(v => [v * 2, String(v * 2)]); //[[2,"2"], [4,"4"], [6,"6"]]
[1,2,3].map(v => [v * 2, String(v * 2)]).flat(); //[2,"2",4,"4",6,"6"]
[1,2,3].flatMap(v => [v * 2, String(v * 2)]); //[2,"2",4,"4",6,"6"]