title: Default values for Vue component props & how to check if a user did not set the prop?
body: <p><strong>1.</strong> How can I set the default value for a component prop in Vue 2? For example, there is a simple <code>movies</code> component that can be used in this way:</p>
  
  <pre><code>&lt;movies year="2016"&gt;&lt;movies&gt;
  
  
  
  Vue.component('movies', {
      props: ['year'],
  
      template: '#movies-template',
      ...
  }
  </code></pre>
  
  <p>But, if a user doesn't specify the <code>year</code>:</p>
  
  <pre><code>&lt;movies&gt;&lt;/movies&gt;
  </code></pre>
  
  <p>then the component will take some default value for the <code>year</code> prop.</p>
  
  <p><strong>2.</strong> Also, what is the best way to check if a user did not set the prop? Is this a good way:</p>
  
  <pre><code>if (this.year != null) {
      // do something
  }
  </code></pre>
  
  <p>or maybe this:</p>
  
  <pre><code>if (!this.year) {
      // do something
  }
  </code></pre>
  
  <p><strong>?</strong></p>