Function observe

06.Router/basic/js/vue.js:2228–2242

* 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. * * @param {*} value * @param {Vue} [vm] * @return {Observer|undefined} * @static

(value, vm)

   */

  function observe(value, vm) {
    if (!value || typeof value !== 'object') {
      return;
    }
    var ob;
    if (hasOwn(value, '__ob__') && value.__ob__ instanceof Observer) {
      ob = value.__ob__;
    } else if (shouldConvert && (isArray(value) || isPlainObject(value)) && Object.isExtensible(value) && !value._isVue) {
      ob = new Observer(value);
    }
    if (ob && vm) {
      ob.addVm(vm);
    }
    return ob;
  }

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