Matrix 2

matrix.js

var Matrix; Matrix = (function(){
	var Constructor = function(inp) {
		this.length = Matrix.getMatrixDims(inp);

		if(!this.length) {
			throw new Error("Invalid matrix");
		}

		this.matrix = inp;
	};

	Constructor.prototype = {
		multiply: function(val) {
			if(!val instanceof Matrix) {
				throw new Error("Invalid matrix");
				return;
			}

			var product = [],
				matrix = this.matrix,
				matrix2 = val.matrix,
				valDims = Matrix.getMatrixDims(matrix2);

			if(!valDims) {
				throw new Error("Invalid matrix");
				return;
			} else if(valDims.x != this.length.y) {
				throw new Error("Incompatible matrices");
				return;
			}

			for(var y=0;y<this.length.y;y++) {
				product[y] = [];

				for(var x=0;x<valDims.x;x++) {
					product[y][x] = 0;

					for(var i=0;i<this.length.x;i++) {
						product[y][x] += matrix[y][i] * matrix2[i][x];
					}
				}
			}

			return product;
		}
	};

	Constructor.getMatrixDims = function(mx) {
		if(typeof mx !== "object" || !mx.length) return false;

		var lens = {
			y: mx.length,
			x: mx[0].length
		};

		for(var i=0;i<mx.length;mx++) {
			if(mx[i].length !== lens.x) {
				return false;
			}
		}
		return lens;
	};

	return Constructor;
})();

module.exports = Matrix;

test.js

const util = require('util');
const Matrix = require('./matrix.js');

var Mx1 = new Matrix([
		[1,2,3],
		[4,5,6]
	]),
	Mx2 = new Matrix([
		[1,2],
		[3,4],
		[5,6]
	]);

var Product = Mx1.multiply(Mx2);

console.log(
	util.inspect(Mx1, false, null)
);
console.log(
	util.inspect(Mx2, false, null)
);
console.log(
	util.inspect(Product, false, null)
);

Example output:

$ node test.js
{ length: { y: 3, x: 3 },
  matrix: [ [ 1, 2, 3 ], [ 4, 5, 6 ], [ 7, 8, 9 ] ] }
{ length: { y: 3, x: 3 },
  matrix: [ [ 2, 2, 2 ], [ 10, 10, 10 ], [ 20, 20, 20 ] ] }
[ [ 82, 82, 82 ], [ 178, 178, 178 ], [ 274, 274, 274 ] ]

$ node test.js
{ length: { y: 2, x: 3 }, matrix: [ [ 1, 2, 3 ], [ 4, 5, 6 ] ] }
{ length: { y: 3, x: 2 },
  matrix: [ [ 1, 2 ], [ 3, 4 ], [ 5, 6 ] ] }
[ [ 22, 28 ], [ 49, 64 ] ]