Why an infinite loop forms in the piece of JavaScript code below?

In the isValid function, when trying to write any line of code in the first for loop, an infinite loop is created. For example when I try console logging i, it just keeps on logging it and never stops.

I guess it has something to do with recursion but i am not able to find exactly why.

The problem is here in the //check same row section

// is Valid
function isValid(board, pos, num){
    //check same row
    for(var i=0; i<9; i++){
      
        // any line here creates problem
        //console.log(i);
      
        if(board[pos[0]][i] == num && i != pos[1]){
            return false;
        }
    }

    //check same column
    for(var i=0; i<9; i++){
        if(board[i][pos[1]] == num && i != pos[0])
            return false;
    }

    //check grid
    var box_x = Math.floor(pos[0]/3);
    var box_y = Math.floor(pos[1]/3);
    for(var i=box_x*3; i<(box_x*3)+3; i++){
        for(var j=box_y*3; j<(box_y*3)+3; j++){
            if(num == board[i][j]){
                return false;
            }
        }
    }

    return true;
}

var board = [
    [8,0,0,0,0,0,0,0,0],
    [0,0,0,2,6,0,0,5,0],
    [0,0,9,8,0,0,0,0,4],
    [7,0,3,0,0,0,0,2,0],
    [0,0,0,0,4,0,0,8,1],
    [5,0,0,0,0,7,0,3,0],
    [0,5,0,0,0,9,2,4,0],
    [0,0,0,7,0,0,0,0,0],
    [9,1,0,0,0,0,0,0,0],
]


// find Empty Cells
function findEmpty(board){
    for(var i=0; i<9; i++){
        for(var j=0; j<9; j++){
            if(board[i][j] == 0){
                var pos = [i, j];
                return pos;
            }
        }
    } 
    var pos = [99,99];
    return pos;
}

//is Valid

function solve(board){
    var pos = findEmpty(board);
    if(pos[0] == 99)
        return true;
    for(var i=1; i<10; i++){
        if(isValid(board, pos, i)){
            board[pos[0]][pos[1]] = i;
            //div_update(pos[0], pos[1], i, board);

            if(solve(board))
                return true;

            board[pos[0]][pos[1]] = 0; //resetting Value
            //div_update(pos[0], pos[1], i, board);
        }
    }
    return false;
}

solve(board);
console.log(board);