Hi Team,

On Lead, we have an Accounts as a Look up, we have a requirement that whenver the user selects an Account, the Company name should be populated with the Account Name in Real time, without saving the record. I have created the below VF page and Extension controller, however not able to achieve the result. Any help is appreciated.

Visualforce Page

<apex:page lightningStylesheets="true" standardController="Lead" extensions="LeadControllerExtension" tabStyle="Lead">
    <apex:form id="form1">
        <apex:sectionheader title="Lead Edit" subtitle="{!if(Lead.Id==null,'New Lead',Lead.Name)}">
        </apex:sectionheader>
        <apex:pageblock mode="edit" id="leadPB" title="Lead Edit">
         <apex:pageblockbuttons >
             <apex:commandbutton action="{!save}" value="Save">
             </apex:commandbutton>
          <apex:commandbutton action="{!cancel}" value="Cancel"></apex:commandbutton>
             </apex:pageblockbuttons>
            <apex:pagemessages ></apex:pagemessages>
            <apex:pageblocksection id="LeadInformationPBS" title="Lead Information">
            <apex:inputfield value="{!Lead.Phone}"></apex:inputfield>
                
            <apex:pageblocksectionitem >
                <apex:outputlabel value="{!$ObjectType.Lead.Fields.FirstName.label}"></apex:outputlabel>
                <apex:outputpanel >
                <apex:inputfield value="{!Lead.Salutation}"></apex:inputfield>
                <apex:inputfield value="{!Lead.FirstName}"></apex:inputfield>
                </apex:outputpanel>
                </apex:pageblocksectionitem>
                <apex:inputfield value="{!Lead.MobilePhone}"></apex:inputfield>
                <apex:inputfield value="{!Lead.LastName}"></apex:inputfield>
                <apex:inputfield value="{!Lead.Fax}"></apex:inputfield>
                <apex:inputField value="{!Lead.Company}">
                <!---<apex:actionSupport event="onchange" action="{!getAcc}" reRender="form1"/> -->
                </apex:inputField>
                                                                <apex:inputfield value="{!Lead.Account__c}">
                  <apex:actionSupport event="onchange" action="{!getAcc}" reRender="{!pageBlockList}"/>
                    <apex:messages />
                </apex:inputfield>
                <apex:inputfield value="{!Lead.Email}"></apex:inputfield>
                <apex:inputfield value="{!Lead.Title}"></apex:inputfield>
                <apex:inputfield value="{!Lead.Website}"></apex:inputfield>
                <apex:inputfield value="{!Lead.Leadsource}"></apex:inputfield>
     <apex:inputfield value="{!Lead.Status}"></apex:inputfield>
                
     <apex:pageblocksection id="AddressInformationPBS" title="Address Information">
                <apex:inputfield value="{!Lead.Street}"></apex:inputfield>
                <apex:outputtext value=""></apex:outputtext>
                <apex:inputfield value="{!Lead.City}"></apex:inputfield>
     <apex:outputtext value=""></apex:outputtext>
                <apex:inputfield value="{!Lead.State}"></apex:inputfield>
     <apex:outputtext value=""></apex:outputtext>
                <apex:inputfield value="{!Lead.PostalCode}"></apex:inputfield>
                <apex:outputtext value=""></apex:outputtext>
                <apex:inputfield value="{!Lead.Country}"></apex:inputfield>
                <apex:outputtext value=""></apex:outputtext>
                                                   
      </apex:pageblocksection>
      </apex:pageblocksection>
         
    </apex:pageblock>
  </apex:form>
       
</apex:page>

Extension Controller:

public with sharing class LeadControllerExtension
{
public Lead LR{get;set;}
public Account con{get;set;}
    
public ApexPages.StandardController stdcntrl{get;set;}
public LeadControllerExtension(ApexPages.StandardController cntrl){
stdcntrl=cntrl;
this.LR = (Lead) stdcntrl.getRecord();
}
    
 public string getAcc(){
     //apexpages.addMessage(new ApexPages.message(ApexPages.Severity.INFO, 'Company Value' ));
//Lead new l1=new Lead();
LR=[Select id,name,Account__c,Company from Lead LIMIT 1];
con=[select name from Account where id= :LR.Account__c];

 LR.Company=con.Name;
return LR.Company;

    }

                }