Calculate properties and listeners

         Concept ： Computing attributes are generally used for more complex operations , Write directly in html The page will appear very bloated , There is the concept of computing attributes . Listeners are derived to assist in computing properties , Perform asynchronous or expensive operations when data changes , Limited choice of listeners .

        When and how ？ This needs continuous accumulation in practical application . There are probably the following scenes ：

        Use calculated properties ：

                1. Data that requires simple mathematical calculations , For example, the little red dot on the shopping cart , You need to calculate the length of the array in the background ~~~

                2. Routing data , For example, carry url~~

                3.vuex The value in , For example, existence vuex The value of the sum of ~~

                4. Changing one of these values will affect the other values ~~ for instance firstname and seconedname, Will affect fullname, Just use the calculation properties

        Using listeners ：

                 1. For asynchronous operation , Choose it first

                 2. Expensive , I don't know how to understand this , You can leave a message if you know

                 3. Changing a value will affect many values , For example, to show firsname, But he was fullname Part of , You can listen with a listener firstname that will do .

My understanding is that .