Transposing a 2D-array in JavaScript

array[0].map((_, colIndex) => array.map(row => row[colIndex]));

map calls a provided callback function once for each element in an array, in order, and constructs a new array from the results. callback is invoked only for indexes of the array which have assigned values; it is not invoked for indexes which have been deleted or which have never been assigned values.

callback is invoked with three arguments: the value of the element, the index of the element, and the Array object being traversed. [source]

here is my implementation in modern browser (without dependency):

transpose = m => m[0].map((x,i) => m.map(x => x[i]))