PnP-JS-Core library contains the number of extensible methods and properties using which we can achieve various actions in a simple code. To know more about this library component, visit the below links:
In this post, we will discuss how  we can get all users from Site Collection using PnP-JS-Core library.
Example
The following code snippet is used to display each user's id and display name from the Site Collection using PnP JavaScript library, click here to read more. 
- <script type="text/javascript" src="/siteassets/scripts/fetch.js"></script>   
- <script type="text/javascript" src="/siteassets/scripts/promise.min.js"></script>   
- <script type="text/javascript" src="/siteassets/scripts/pnp.min.js"></script>  
-    
- <div id="sample"></div>  
-    
- <script type="text/javascript">  
-   
- $pnp.sp.web.siteUsers.get().then(function(data) {  
-     var users = "";  
-     for (var i = 0; i < data.length; i++) {  
-         users += data[i].Id + " - " + data[i].Title + "<br/>";  
-     }  
-     document.getElementById("sample").innerHTML = users;  
- });  
- </script>