krahets/hello-algo · error · Error

Stack is empty

Error message

Stack is empty

What it means

Thrown by ArrayStack.pop when the stack is empty. pop calls Array.pop on the backing array, but the guard ensures the caller never receives undefined masquerading as a number and signals the precondition failure explicitly.

Source

Thrown at en/codes/typescript/chapter_stack_and_queue/array_stack.ts:31

    /* Get the length of the stack */
    get size(): number {
        return this.stack.length;
    }

    /* Check if the stack is empty */
    isEmpty(): boolean {
        return this.stack.length === 0;
    }

    /* Push */
    push(num: number): void {
        this.stack.push(num);
    }

    /* Pop */
    pop(): number | undefined {
        if (this.isEmpty()) throw new Error('Stack is empty');
        return this.stack.pop();
    }

    /* Return list for printing */
    top(): number | undefined {
        if (this.isEmpty()) throw new Error('Stack is empty');
        return this.stack[this.stack.length - 1];
    }

    /* Return Array */
    toArray() {
        return this.stack;
    }
}

/* Driver Code */
/* Access top of the stack element */
const stack = new ArrayStack();

View on GitHub (pinned to 69932aed18)

Solutions

1. Check isEmpty() before pop.
2. Use while (!stack.isEmpty()) for draining.
3. Wrap pop to return undefined on empty instead of throwing.

Example fix

// before
const v = stack.pop(); // throws if empty

// after
const v = stack.isEmpty() ? undefined : stack.pop();

const v = stack.isEmpty() ? undefined : stack.pop();

function hasElements(s) { return typeof s.isEmpty === 'function' && !s.isEmpty(); }

try { return stack.pop(); }
catch (e) { if (!/Stack is empty/.test(e.message)) throw e; return undefined; }

When it happens

Trigger: Calling pop on a freshly created stack; popping more times than you pushed; unbalanced push/pop in expression evaluation.

Common situations: Algorithm implementations (e.g. parenthesis matching, DFS) that pop without checking depth; loops that assume the stack is non-empty.

Related errors

• Stack is empty
• 栈为空
• 栈为空
• Heap is empty.
• The Deque Is Empty.

AI-assisted analysis of krahets/hello-algo@69932aed18 (2026-08-13). Data as JSON: /api/errors/797b1973e7b23ada. Report an issue: GitHub.