Meituan-Dianping/mpvue · warning

Invalid handler for event "${event.name}": got ${String(cur)

Error message

Invalid handler for event "${event.name}": got ${String(cur)}

What it means

During vnode update, an entry in the `on` listeners object is `undefined`/`null`, meaning the component asked to listen to an event but supplied no handler function. Vue warns and skips attaching the listener.

Source

Thrown at src/core/vdom/helpers/update-listeners.js:56

  }
  invoker.fns = fns
  return invoker
}

export function updateListeners (
  on: Object,
  oldOn: Object,
  add: Function,
  remove: Function,
  vm: Component
) {
  let name, cur, old, event
  for (name in on) {
    cur = on[name]
    old = oldOn[name]
    event = normalizeEvent(name)
    if (isUndef(cur)) {
      process.env.NODE_ENV !== 'production' && warn(
        `Invalid handler for event "${event.name}": got ` + String(cur),
        vm
      )
    } else if (isUndef(old)) {
      if (isUndef(cur.fns)) {
        cur = on[name] = createFnInvoker(cur)
      }
      add(event.name, cur, event.once, event.capture, event.passive)
    } else if (cur !== old) {
      old.fns = cur
      on[name] = old
    }
  }
  for (name in oldOn) {
    if (isUndef(on[name])) {
      event = normalizeEvent(name)
      remove(event.name, oldOn[name], event.capture)
    }

View on GitHub (pinned to 6c5d78ee04)

Solutions

1. Remove the listener key entirely when there is no handler, instead of setting it to undefined
2. Guard with a fallback: `on: { click: this.onClick || (() => {}) }`
3. Filter out falsy handlers before passing: `on: Object.fromEntries(Object.entries(handlers).filter(([, fn]) => fn))`
4. Fix misspelled handler references

Example fix

// before
h('input', { on: { input: props.onInput } }) // onInput may be undefined
// after
const handlers = {}
if (props.onInput) handlers.input = props.onInput
h('input', { on: handlers })

function validOn (on) {
  const out = {}
  for (const k in on) if (typeof on[k] === 'function') out[k] = on[k]
  return out
}
// usage: h(Comp, { on: validOn(handlers) })

function isHandler (fn) { return typeof fn === 'function' }

When it happens

Trigger: `h(MyComp, { on: { click: undefined } })`; spreading an object of handlers where a key exists but its value is undefined; building `on` from reactive data where a handler is conditionally absent.

Common situations: Dynamically assembling listener maps in render functions; destructuring props that lack a handler; TypeScript-less code where a handler name is misspelled and resolves to undefined.

Related errors

• Avoid using observed data object as vnode data: ${JSON.strin
• Avoid using observed data object as vnode data: ${JSON.strin
• Avoid using non-primitive value as key, use string/number va
• Duplicate presence of slot "${name}" found in the same rende
• Avoid using non-primitive value as key, use string/number va

AI-assisted analysis of Meituan-Dianping/mpvue@6c5d78ee04 (2026-09-02). Data as JSON: /api/errors/abe2f3c6a3809f1d. Report an issue: GitHub.