[Endy]

var f = prompt('Vals 1!', '2,7,6').split(','),
    s = prompt('Vals 2!', '9,5,1').split(','),
    t = prompt('Vals 3!', '4,3,8').split(',');

alert(isMagic([f, s, t]));

function isMagic(matrix) {
    for (var i = 0; i < matrix.length; i++) {
        var e = matrix[i];
        for (var j = 0; j < e.length; j++) {
            e[j] = +e[j];
        }
    }
    var diagonals = [
        [],
        []
    ],
        rows = [],
        cols = [
            [],
            [],
            []
        ];

    for (var i = 0; i < matrix.length; i++) {
        var e = matrix[i],
            rSum = 0;
        for (var j = 0; j < e.length; j++) {
            rSum += e[j];
        }
        rows.push(rSum);
        diagonals[0].push(e[i]);
        cols[0].push(e[0]);
        cols[1].push(e[1]);
        cols[2].push(e[2]);
    }

    var count = 1;
    for (var i = 0; i < matrix.length; i++) {
        var e = matrix[i]
        diagonals[1].push(e[e.length - count]);
        count++;
    }
    for (var i = 0; i < cols.length; i++) {
        var e = cols[i],
            s = 0;
        for (var j = 0; j < e.length; j++) {
            s += e[j];
        }
        cols[i] = s;
    }

    for (var i = 0; i < diagonals.length; i++) {
        var e = diagonals[i],
            s = 0;
        for (var j = 0; j < e.length; j++) {
            s += e[j];
        }
        diagonals[i] = s;
    }
    if (diagonals[0] == diagonals[1] && rows[0] == rows[1] && rows[1] == rows[2] && cols[0] == cols[1] && cols[1] == cols[2]) {
        return 'Magic square';
    };
    return false;
};