title: How to create a common service throughout the app in angular4
body: <p>I need a common service in all of the other services. The common service will be initiated one time only.</p>
  
  <p>Lets say the common service is - </p>
  
  <pre><code>export Class CommonService
  {
       _commonVar1= "";
       _commonVar2= "";
  }
  </code></pre>
  
  <p>now the instance of common service is needed among all other services. Remember - the commonservice will be initiated one time only.</p>