krahets/hello-algo · error · Error

栈为空

Error message

栈为空

What it means

Thrown by peek() on a singly-linked-list-backed stack when the internal #stackPeek is null (no nodes). peek() returns #stackPeek.val, which would throw a TypeError without the guard. pop() calls peek() first, so both surface the same error. The check is reference-based (!#stackPeek), equivalent to size === 0.

Source

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

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

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

    /* 访问栈顶元素 */
    peek() {
        if (!this.#stackPeek) throw new Error('栈为空');
        return this.#stackPeek.val;
    }

    /* 将链表转化为 Array 并返回 */
    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 */
/* 初始化栈 */
const stack = new LinkedListStack();

View on GitHub (pinned to 69932aed18)

Solutions

1. Guard: if (stack.size > 0) stack.peek(); (the class exposes size via a getter).
2. Push a sentinel node for algorithms that assume a non-empty stack.
3. Wrap in a helper returning null on empty rather than catching the throw.
4. Track push/pop counts and assert balanced usage in tests.

Example fix

// before
const t = stack.peek(); // throws if empty
// after
const t = stack.size > 0 ? stack.peek() : null;

function safePeek(stack) {
  return stack.size > 0 ? stack.peek() : null;
}

function stackNotEmpty(stack) {
  return stack.size > 0;
}

try {
  const t = stack.peek();
} catch (e) {
  if (e instanceof Error && e.message === '栈为空') { /* empty stack */ } else throw e;
}

When it happens

Trigger: Calling peek()/pop() on a freshly constructed stack; popping the last node then peeking again; DFS/backtracking unwind past the bottom; balanced-symbol checks on an empty input.

Common situations: Monotonic-stack top inspection before any push; expression evaluation with leading operators; recursive helpers that peek before pushing.

Related errors

• Stack is empty
• スタックが空
• 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/9f5f1574a3e24491. Report an issue: GitHub.