title: Simple Vue.js Computed Properties Clarification
body: <p>I'm not new to Vue.js, but I'm going through the docs again, trying to pick up on anything I missed the first time. I came across this statement in <a href="https://v2.vuejs.org/v2/guide/computed.html#Basic-Example" rel="nofollow noreferrer">basic example section of using computed properties</a>:</p>
  <blockquote>
  <p>You can data-bind to computed properties in templates just like a normal property. Vue is aware that <code>vm.reversedMessage</code> depends on <code>vm.message</code>, so it will update any bindings that depend on <code>vm.reversedMessage</code> when <code>vm.message</code> changes. And the best part is that <strong>we’ve created this dependency relationship declaratively: the computed getter function has no side effects</strong>, which makes it easier to test and understand.</p>
  </blockquote>
  <hr />
  <p>The part about <strong>we’ve created this dependency relationship declaratively: the computed getter function has no side effects</strong>, isn't clear to me. I do understand that a side effect is some action happening that is not directly related to the pure intentions of the function, but I'm not clear how it's being used in this statement.</p>
  <p>Could someone explain further what the opposite could be? What are the potential side effects that could be happening?</p>