console.log output is wrong for multidimensional arrays

var a = [[1,2,3,4], [5,6,7,8]];
console.log("array (raw):", a);

console.log("array (string):", JSON.stringify(a));

qml: array (raw): [1,2,3,4,5,6,7,8] 
qml: array (string): [[1,2,3,4],[5,6,7,8]]}}

array (raw): [ [ 1, 2, 3, 4 ], [ 5, 6, 7, 8 ] ]
array (string): [[1,2,3,4],[5,6,7,8]]