Carry out the following steps to develop a Lightning JavaScript Controller, which is used for event handling and function definition for the Lightning Component, using the Salesforce Developer Console:

1. Click on the Setup gear icon, as shown in the following screenshot:

The Setup gear icon is located in the top right-hand area of the main Home page.

2. Click the Developer Console option as shown in the following screenshot:

3. In the resulting Developer Console window, open the resource or click on the tab for the Lightning Component accountSearchBeforeCreate.cmp.
4. Click on CONTROLLER (or press Ctrl + Shift + 2), as shown in the following screenshot:

5. In the resulting Lightning JavaScript Controller edit page, paste the following code:

 
({ // Search for account record 
   onSearch: function(component, event, helper) { 
     var searchKeyFld = component.find("searchId"); 
     var srcValue = searchKeyFld.get("v.value"); 
     if (srcValue == '' || srcValue == null) { 
       // Display an error nothing entered 
       searchKeyFld.set("v.errors", [{ 
       message: "Please enter an account name before
       searching..." 
       }]); 
       } else {earchKeyFld.set("v.errors", null); 
       // Call the accountSearchBeforeCreateHelper method 
       helper.SearchHelper(component, event); 
       } 
       }, 
 
       // Navigate to account record 
       onNavigate : function (component, event, helper) { 
     
       // Retrieve the selected account record  
       var selectedItem = event.currentTarget; 
       var index = selectedItem.dataset.record; 
       var accObject = component.get("v.searchResult")[index]; 
       var navEvt = $A.get("e.force:navigateToSObject"); 
        navEvt.setParams({"recordId": accObject.Id, 
        "slideDevName": "detail" 
        }); 
        navEvt.fire(); 
       }, 
     
   onCreate : function (component, event, helper) { 
    // Recordtype selection handler 
    var sRecordTypeId = null; // default 
    var RCT_STR = 'recordTypeId'; 
    var RCT_LEN = RCT_STR.length + 1; 
    var SID_LEN = 15; 
    var TOT_LEN = RCT_LEN + SID_LEN; 
    var url_string = window.location.href; 
         
    // Main account creation 
    var createRecordEvent = $A.get("e.force:createRecord"); 
    var sSearch = component.get("v.searchString"); 
     
    // Getting the record type if present null if not present 
    var isRct = url_string.includes(RCT_STR);               
      if(isRct=== true){ 
        sRecordTypeId = url_string.substring( 
        url_string.indexOf(RCT_STR) + RCT_LEN, 
        url_string.indexOf(RCT_STR) + TOT_LEN); 
      }         
      createRecordEvent.setParams({ 
            "entityApiName": "Account", 
            "recordTypeId" : sRecordTypeId, 
            "defaultFieldValues": { 
            "Name"     : sSearch 
            } 
      }); 
      createRecordEvent.fire(); 
   }     
})

6. Click on File.
7. Click on Save, as shown in the following screenshot: