DOMMatrixReadOnly - Web APIs
(in other words, down the first column from top to bottom, then the second column, and so forth.) dommatrixreadonly.tofloat64array() returns a new float64array containing all 16 elements (m11, m12, m13, m14, m21, m22, m23, m24, m31, m32, m33, m34, m41, m42, m43, m44) which comprise the matrix.