js: matrix multiplication using dot product and transposition

mm.js

mmultiply = function(a,b) {
	return a.map(function(x,i) {
		return transpose(b).map(function(y,k) {
			return dotproduct(x, y)
		});
	});
}

dotproduct = function(a,b) {
	return a.map(function(x,i) {
		return a[i] * b[i];
	}).reduce(function(m,n) { return m + n; });
}

transpose = function(a) {
	return a[0].map(function(x,i) {
		return a.map(function(y,k) {
			return y[i];
		})
	});
}

a = [[1,2,3],[4,5,6]]
b = [[7,8],[9,10],[11,12]]

c = [[1,2,3],[4,5,6],[7,8,9]]
d = [[10,11,12],[13,14,15],[16,17,18]]

JSON.stringify(mmultiply(a,b)) // "[[58,64],[139,154]]"
JSON.stringify(mmultiply(c,d)) // "[[84,90,96],[201,216,231],[318,342,366]]"

guy. i've to thanks you, like a lot! I've past at least 3/4hours to create this function to get the dot product of two array. the problem is that it don't worked with all array. so, your function save me from going crazy and nearly give up. thankkks