I have a Description field of type Long Text Area. I'm trying to get the first few lines to display. 
1. I tried creating a formula field 

    LEFT(Description, 500) 
I get Error: You referenced an unsupported field type called "Long Text Area" using the following field: Description. 
2.I tried using SOQL but I couldn't get it to work. 
3.I also tried something like 

     <apex:outputText value="{!LEFT(GoodMorning,4)}"/> 
I got the following error : Failed to save HighlightComponent.cmp: c:HighlightComponent:26,75: No function found for key: LEFT: Source

How can I get a substring of the description field to show up in a custom lightning component. Here's my code: 

Controller 

    public class HighlightComponentController {
    @AuraEnabled        
    
        public static List<Case> findCase (Id recordId) {
            List<Case> details = [SELECT CaseNumber, OwnerId, Description 
                                 FROM Case WHERE Id=:recordId];
            
            return details;
        }
        
        String description { get; private set; }

        public String truncatedDescription
        {
            get
            {
                return (description == null) ? null : description.abbreviate(3);
            }
        }
        
    }

Component 

    <aura:attribute name="truncatedDescription" type="String" />
      <p><lightning:formattedText value="{!v.truncatedDescription}"/></p>

Javascript

    {
      doInit : function(component, event, helper) {
        var action = component.get("c.findCase");
        action.setParams({
            recordId: component.get("v.recordId")
        });
        action.setCallback(this, function(data) {
            component.set("v.details", data.getReturnValue());
        });
        $A.enqueueAction(action);
        
        var action2 = component.get("c.truncatedDescription");
       
        action2.setCallback(this, function(data) {
            component.set("v.truncatedDescription", data.getReturnValue());
        });
        $A.enqueueAction(action2);
    }