krahets/hello-algo · error · Error

スタックが空

Error message

スタックが空

What it means

Thrown by the linked-list stack's peek when the stack pointer (#stackPeek) is null/undefined, i.e. the stack is empty. peek reads #stackPeek.val; the guard converts what would be a TypeError (reading .val of null) into a clear domain error. pop() calls peek() first, so popping an empty stack surfaces the same message.

Source

Thrown at ja/codes/javascript/chapter_stack_and_queue/linkedlist_stack.js:46

    /* プッシュ */
    push(num) {
        const node = new ListNode(num);
        node.next = this.#stackPeek;
        this.#stackPeek = node;
        this.#stkSize++;
    }

    /* ポップ */
    pop() {
        const num = this.peek();
        this.#stackPeek = this.#stackPeek.next;
        this.#stkSize--;
        return num;
    }

    /* スタックトップの要素にアクセス */
    peek() {
        if (!this.#stackPeek) throw new Error('スタックが空');
        return this.#stackPeek.val;
    }

    /* 連結リストを Array に変換して返す */
    toArray() {
        let node = this.#stackPeek;
        const res = new Array(this.size);
        for (let i = res.length - 1; i >= 0; i--) {
            res[i] = node.val;
            node = node.next;
        }
        return res;
    }
}

/* Driver Code */
/* スタックを初期化 */
const stack = new LinkedListStack();

View on GitHub (pinned to 69932aed18)

Solutions

1. Check !stack.isEmpty() (or #stackPeek presence via an exposed method) before peek()/pop().
2. Use while (!stack.isEmpty()) for drain loops.
3. Return a sentinel when empty instead of throwing.
4. Keep push/pop counts balanced.

Example fix

// before
const top = stack.peek();  // throws if empty

// after
const top = stack.isEmpty() ? null : stack.peek();

function safePeek(stack) {
  return stack.isEmpty() ? null : stack.peek();
}

const isNonEmpty = (s) => typeof s.isEmpty === 'function' && !s.isEmpty();

try {
  return stack.peek();
} catch (e) {
  if (e instanceof Error && e.message === 'スタックが空') return null;
  throw e;
}

When it happens

Trigger: Calling peek() or pop() on an empty stack (no pushes, or fully popped); calling after #stackPeek was reset to null.

Common situations: Unbalanced push/pop in algorithms; peeking before the first push; recursion-simulation stacks that drain.

Related errors

• 栈为空
• Stack is empty
• стек пуст
• 堆疊為空
• 栈为空

AI-assisted analysis of krahets/hello-algo@69932aed18 (2026-08-13). Data as JSON: /api/errors/0c44a16d34f8ba4b. Report an issue: GitHub.