Flatten an array with ES6

using-Array.prototype.flat().js

const multiDimensionalArray = [ [1, 2], [3, 4], [5, 6] ];
const flattenedArray =multiDimensionalArray.flat();
console.log(flattenedArray) // [1, 2, 3, 4, 5, 6]

// This methods accepts one argument to choose the depth of the flattening.
const multiDimensionalArray = [[ [1, 2]], [3, 4], [5, 6] ];
multiDimensionalArray.flat(2);
console.log(flattenedArray) // [1, 2, 3, 4, 5, 6]

using-the-spread-operator.js

const multiDimensionalArray = [ [1, 2], [3, 4], [5, 6] ]; 
const flattenedArray = [].concat(…multiDimensionalArray); 
console.log(flattenedArray) // [1, 2, 3, 4, 5, 6]