function solution(n) {
    
    let answer = [];
    for(let i = 1; i<= n; i++) {
        answer.push(Array.from({length: i}, () => 0));
    }
    
    let startRow = 0;
    let startColumn = 0;
    let endRow = n-1;
    let endColumn = n-1;
    let cnt = 0;
    let num = 1;
    
    while(startRow <= endRow && startColumn <= endColumn) {
        for(let i = startRow; i <= endRow; i++) {
            answer[i][startColumn] = num;
            num++
        }
        startRow++;
        startColumn++;
    
        for(let i = startColumn; i <= endColumn; i++) {
            answer[endRow][i] = num;
            num++
        }
        endColumn--;
        endRow--;
        for(let i = endRow; i>= startRow; i--) {
            answer[i][answer[i].length -1 -cnt] = num;
            num++;
        }
        startRow++;
        endColumn--;
        cnt++;   
    }
    return answer.flat()
}

참고

https://velog.io/@proshy/%ED%94%84%EB%A1%9C%EA%B7%B8%EB%9E%98%EB%A8%B8%EC%8A%A4javascript-%EC%82%BC%EA%B0%81-%EB%8B%AC%ED%8C%BD%EC%9D%B4