HTML snippet is used to retrieve the creation date and modified date of a web site using JSOM

getwebdetails.html

<!-- How to get the Created date and Last Modified date of a Site -->  
<!-- HTML Content -->    
<div id="myapp"></div>    
<!-- Script Content -->    
<script type='text/javascript'>    
var oWeb;    
function getwebdetails()     
{    
    var clientContext = SP.ClientContext.get_current(); // equivalent to SPContext.Current    
    oWeb = clientContext.get_web(); //Gets the current Web Object    
    //clientContext.load(oWeb); - Load all properties for a web  
    clientContext.load(oWeb,'Title', 'Created', 'LastItemModifiedDate');     
    clientContext.executeQueryAsync(onSucceeded,onFailed);    
}    
function onSucceeded()    
{    
    var strmsg = "";  
    strmsg += "<b>Web Title:</b> " + oWeb.get_title() +"<br/>";  
    strmsg += "Created Date: "+ oWeb.get_created()+"<br/>";  
    strmsg += "Last Modified Date: "+ oWeb.get_lastItemModifiedDate();  
  
    document.getElementById("myapp").innerHTML = strmsg;  
}    
function onFailed(sender, args)    
{    
    try    
    {    
        console.log('Error: ' + args.get_message());    
    }     
    catch (err)     
    {    
    }    
}    
ExecuteOrDelayUntilScriptLoaded(getwebdetails, "sp.js");    
</script>