//We have the following array:

let arr1 = ["it's Sunny in", "", "London"];

​

//Map creates multidimensional array:

arr1.map(item => item.split(" "));

//returns

(3) [Array(3), Array(1), Array(1)]

  0: (3) ["it's", "Sunny", "in"]

  1: [""]

  2: ["London"]

// visually: [["it's", "Sunny", "in"], [""], ["London"]]

​

//While flatmap makes an array flattened to dimension 1 (“unidimensional” so to say):

arr1.flatMap(item => item.split(" "));

//returns

(5) ["it's", "Sunny", "in", "", "London"]

  0: "it's"

  1: "Sunny"

  2: "in"

  3: ""

  4: "London"

//visually: ["it's", "Sunny", "in", "", "London"]