Meituan-Dianping/mpvue · error

v-once can only be used inside v-for that is keyed.

Error message

v-once can only be used inside v-for that is keyed. 

What it means

Dev-only codegen warning from genOnce: v-once was applied to a node inside a v-for that has no key on any ancestor v-for. The _o() once-cache marker needs the enclosing for's key to key cached static nodes; without it the compiler warns and emits the node as a normal (non-once) element.

Source

Thrown at src/compiler/codegen/index.js:111

}

// v-once
function genOnce (el: ASTElement, state: CodegenState): string {
  el.onceProcessed = true
  if (el.if && !el.ifProcessed) {
    return genIf(el, state)
  } else if (el.staticInFor) {
    let key = ''
    let parent = el.parent
    while (parent) {
      if (parent.for) {
        key = parent.key
        break
      }
      parent = parent.parent
    }
    if (!key) {
      process.env.NODE_ENV !== 'production' && state.warn(
        `v-once can only be used inside v-for that is keyed. `
      )
      return genElement(el, state)
    }
    return `_o(${genElement(el, state)},${state.onceId++}${key ? `,${key}` : ``})`
  } else {
    return genStatic(el, state)
  }
}

export function genIf (
  el: any,
  state: CodegenState,
  altGen?: Function,
  altEmpty?: string
): string {
  el.ifProcessed = true // avoid recursion
  return genIfConditions(el.ifConditions.slice(), state, altGen, altEmpty)

View on GitHub (pinned to 6c5d78ee04)

Solutions

1. Add a unique :key to the v-for containing the v-once element
2. Remove v-once from that node if per-item re-render is intended

When it happens

Trigger: Thrown at src/compiler/codegen/index.js:111 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/fd0265c8ef570a45. Report an issue: GitHub.