[nerv_]

/**
 * @see [url]https://ru.wikipedia.org/wiki/Магический_квадрат[/url]
 * @param {Array<Array<Number>>} matrix
 * @constructor
 */
function Square(matrix) {
    this.__matrix = matrix;
}

/**
 * @returns {Boolean}
 */
Square.prototype.isMagic = function() {
    var lastRow = this.__matrix.length - 1;
    var lastColumn = this.__matrix[0].length - 1;
    var magicConst = this.getMagicConst();
    for(var i = 0; i <= lastRow; i++) {
        if (this.__calcSum(i, 0, 0, 1, i, lastColumn) !== magicConst) return false;
    }
    for(var j = 0; j <= lastColumn; j++) {
        if(this.__calcSum(0, j, 1, 0, lastRow, j) !== magicConst) return false;
    }
    if(this.__calcSum(0, 0, 1, 1, lastRow, lastColumn) !== magicConst) return false;
    if(this.__calcSum(lastRow, 0, -1, 1, 0, lastColumn) !== magicConst) return false;
    return true;
};
/**
 * @returns {Number}
 */
Square.prototype.getMagicConst = function() {
    var k = this.__matrix.length;
    return (k * (k * k + 1)) / 2;
};
/**
 * @param {Number} rowStart
 * @param {Number} colStart
 * @param {Number} rowStep
 * @param {Number} colStep
 * @param {Number} rowEnd
 * @param {Number} colEnd
 * @returns {Number}
 * @private
 */
Square.prototype.__calcSum = function(rowStart, colStart, rowStep, colStep, rowEnd, colEnd) {
    var min = Math.min;
    var max = Math.max;
    var limitRow = rowStep > 0 ? min : max;
    var limitCol = colEnd > 0 ? min : max;
    var i = limitRow(rowStart - rowStep, rowEnd);
    var j = limitCol(colStart - colStep, colEnd);
    var sum = 0;
    while(i !== rowEnd || j !== colEnd) {
        i = limitRow(i + rowStep, rowEnd);
        j = limitCol(j + colStep, colEnd);
        sum += this.__matrix[i][j];
    }
    return sum;
};


// ------------------------


var matrix = [
    [2, 7, 6],
    [9, 5, 1],
    [4, 3, 8]
];

var square = new Square(matrix);

alert(square.isMagic());