Here I have an async function in javascript that is used to fill up the sudoku board with numbers (basically its solution). I used a sleeper function between each number insertion so that the user can get a better feel of the recursion and backtracking algorithm, however after the fifteenth number gets inserted, the function stops by itself... What is going on here exactly ?

var finalInd;

function sleep() {
    console.log("happy")
    return new Promise(resolve => setTimeout(resolve, 100));
}


async function solve () {

    allowed = false;
    var empty = findEmptySpace();

    if(!empty) {
        return true;
    }

    for(let i=1; i<10; i  ) {

        if(checkDuplicates(board, i, empty)) {

            board[empty[0]][empty[1]] = i;
            finalInd = (empty[0]*9)   empty[1];

            await sleep()
            funcId("board").children[finalInd].innerHTML = i;

            if(solve(board)) {
                return true;
            }
            
            board[empty[0]][empty[1]] = 0;
            
            funcId("board").children[finalInd].innerHTML = 0;
        }
    }

    funcId("board").children[0].innerHTML = board[0][0];
    return false;

}


function checkDuplicates (board, num, empty) {
    for(let i=0; i<9; i  ) {
        if(board[empty[0]][i] == num && empty[1] != i) {
            return false;
        }
    }

    for(let i=0; i<9; i  ) {
        if(board[i][empty[1]] == num && empty[0] != i) {
            return false;
        }
    }

    var x = Math.floor(empty[1]/3);
    var y = Math.floor(empty[0]/3);

    for(let i=(y*3); i<(y*3) 3; i  ) {
        for(let j=(x*3); j<(x*3) 3; j  ) {
            if(board[i][j] == num && i != empty[0] && j != empty[1]) {
                return false;
            }
        }
    }

    return true;

}


function findEmptySpace () {

    for(let i=0; i<9; i  ) {
        for(let j=0; j<9; j  ) {
            if(board[i][j] == 0) {
                return [i, j];
            }
        }
    }

}

CodePudding user response：

I think you forgot to await the recursive call to solve, so it will always return a promise, which it's truthy, and your function will terminate.