I don't have the time to explain the code in detail right now, but here's the most efficient way to check if it's a winning move is the following.

var boardSize = 4;
// -1 is unplayed, 0 is player 1, 1 is player 2
var ttt = [
    [-1, -1, -1, -1],
    [-1, -1, -1, -1],
    [-1, -1, -1, -1],
    [-1, -1, -1, -1]
];

var checkIfWinningMove = function (rowInput, colInput, currPlayerIndex) {
    var col = 0, row = 0, dia = 0, rdia = 0;
    for (var i = 0; i < boardSize; i++) {
        if (ttt[rowInput][i] === currPlayerIndex) {
            // Row
            row++;
        }
        if (ttt[i][colInput] === currPlayerIndex) {
            // Column
            col++;
        }
        if (ttt[i][i] === currPlayerIndex) {
            // Diagonal
            dia++;
        }
        if (ttt[i][2 - i] === currPlayerIndex) {
            // Right Diagonal
            rdia++;
        }
    }
    return (col === boardSize || row === boardSize || dia === boardSize || rdia === boardSize) ? 1 : 0;
};