Meituan-Dianping/mpvue · error

The data property "${key}" is already declared as a prop. Us

Error message

The data property "${key}" is already declared as a prop. Use prop default value instead.

What it means

Raised in initData when a data key also exists in the props option. Props are initialized before data and proxied on the instance first, so the data entry would collide with the prop binding; moreover props are owned by the parent and re-supplied on every parent re-render, making the local data value unreachable. Vue skips proxying the data key, and the prop's value (or its default) is what the instance actually reads.

Source

Thrown at src/core/instance/state.js:145

    )
  }
  // proxy data on instance
  const keys = Object.keys(data)
  const props = vm.$options.props
  const methods = vm.$options.methods
  let i = keys.length
  while (i--) {
    const key = keys[i]
    if (process.env.NODE_ENV !== 'production') {
      if (methods && hasOwn(methods, key)) {
        warn(
          `method "${key}" has already been defined as a data property.`,
          vm
        )
      }
    }
    if (props && hasOwn(props, key)) {
      process.env.NODE_ENV !== 'production' && warn(
        `The data property "${key}" is already declared as a prop. ` +
        `Use prop default value instead.`,
        vm
      )
    } else if (!isReserved(key)) {
      proxy(vm, `_data`, key)
    }
  }
  // observe data
  observe(data, true /* asRootData */)
}

function getData (data: Function, vm: Component): any {
  try {
    return data.call(vm)
  } catch (e) {
    handleError(e, vm, `data()`)
    return {}

View on GitHub (pinned to 6c5d78ee04)

Solutions

1. Remove the duplicated key from data and rely on the prop, declaring a prop default if a fallback value is needed
2. If the component needs a locally mutable version, keep the prop and add a differently-named data property initialized from it

When it happens

Trigger: Thrown at src/core/instance/state.js:145 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of Meituan-Dianping/mpvue@6c5d78ee04 (2026-09-02). Data as JSON: /api/errors/7ac0b795a518dfe7. Report an issue: GitHub.