js how to flat arr code example

Example 1: javascript array flat

var arr1 = [1, 2, [3, 4]];
arr1.flat(); 
// [1, 2, 3, 4]

var arr2 = [1, 2, [3, 4, [5, 6]]];
arr2.flat();
// [1, 2, 3, 4, [5, 6]]

var arr3 = [1, 2, [3, 4, [5, 6]]];
arr3.flat(2);
// [1, 2, 3, 4, 5, 6]

Example 2: Javascript flatten array of arrays

var multiDimensionArray = [["a"],["b","c"],["d"]]; //array of arrays
var flatArray = Array.prototype.concat.apply([], multiDimensionArray); //flatten array of arrays
console.log(flatArray); // [ "a","b","c","d"];