Function genOnce

static/vuejs/vue.common.js:8549–8573

(el)

// v-once
function genOnce (el) {
  el.onceProcessed = true;
  if (el.if && !el.ifProcessed) {
    return genIf(el)
  } else if (el.staticInFor) {
    var key = '';
    var parent = el.parent;
    while (parent) {
      if (parent.for) {
        key = parent.key;
        break
      }
      parent = parent.parent;
    }
    if (!key) {
      process.env.NODE_ENV !== 'production' && warn$3(
        "v-once can only be used inside v-for that is keyed. "
      );
      return genElement(el)
    }
    return ("_o(" + (genElement(el)) + "," + (onceCount++) + (key ? ("," + key) : "") + ")")
  } else {
    return genStatic(el)
  }
}

function genIf (el) {
  el.ifProcessed = true; // avoid recursion