Solve a system of 8 equations in js

Given 8 equations and 16 unknowns or a 4x4 matrix grid


var x = [];

x[0] = a[0][0] + a[0][1] + a[0][2] + a[0][3];
x[1] = a[1][0] + a[1][1] + a[1][2] + a[1][3];
x[2] = a[2][0] + a[2][1] + a[2][2] + a[2][3];
x[3] = a[3][0] + a[3][1] + a[3][2] + a[3][3];

var y = [];

y[0] = a[0][0] + a[1][0] + a[2][0] + a[3][0];
y[1] = a[0][1] + a[1][1] + a[2][1] + a[3][1];
y[2] = a[0][2] + a[1][2] + a[2][2] + a[3][2];
y[3] = a[0][3] + a[1][3] + a[2][3] + a[3][3];

return [x, y];

from [x, y] create a function returning array a