Function observe

m3u8/vue.js:988–1008

* Attempt to create an observer instance for a value, * returns the new observer if successfully observed, * or the existing observer if the value already has one.

(value, asRootData)

   * or the existing observer if the value already has one.
   */
  function observe (value, asRootData) {
    if (!isObject(value) || value instanceof VNode) {
      return
    }
    var ob;
    if (hasOwn(value, '__ob__') && value.__ob__ instanceof Observer) {
      ob = value.__ob__;
    } else if (
      shouldObserve &&
      !isServerRendering() &&
      (Array.isArray(value) || isPlainObject(value)) &&
      Object.isExtensible(value) &&
      !value._isVue
    ) {
      ob = new Observer(value);
    }
    if (asRootData && ob) {
      ob.vmCount++;
    }
    return ob
  }

  /**
   * Define a reactive property on an Object.