Comparing JavaScript Remoting and

The <apex:actionFunction> component also lets you call controller action methods through JavaScript.

In general, <apex:actionFunction> is easier to use and requires less code, while JavaScript remoting offers more flexibility.

Here are some specific differences between the two.

• The <apex:actionFunction> tag:
  • lets you specify rerender targets
  • submits the form
  • doesn’t require you to write any JavaScript
• JavaScript remoting:
• lets you pass parameters
• provides a callback
• requires you to write some JavaScript

Both JS Remoting and Action Function call the class's methods that are linked to VF page.

VLOOKUP

Returns a value by looking up a related value on a custom object similar to the VLOOKUP() Excel function

1.       VLOOKUP only available on Custom Objects.

2.       VLOOKUP only available in Validation Rules.

3.       VLOOKUP can only be done on the Name fields.

4.       The field_to_return must be an auto number, roll-up summary, lookup relationship, master-detail relationship, checkbox, date, date/time, email, number, percent, phone, picklist, text, text area, orURL field type.

5.       The field_on_lookup_object must be the Record Name field on a custom object.

6.       The field_on_lookup_object and lookup_value must be the same data type.

7.       If more than one record matches, the value from the first record is returned.

8.       The value returned must be on a custom object.

9.       You cannot delete the custom field or custom object referenced in this function.

E.g.

A simple validation on a Custom Object Invoice__c.

Here vlookup function matches invoice name to value ‘krrish’ if found duplicate then it returns testValues_c field value  of first matches record.

Name=VLOOKUP( $ObjectType.krrish__Invoice__c.Fields.krrish__testValues__c,  $ObjectType.krrish__Invoice__c.Fields.Name,"krrish" )

What is SYSTEM in Salesforce?

System

• System is a namespace
• System is a class in System namespace

The System namespace provides classes and methods for core Apex functionality.

The System namespace is auto included in Salesforce Orgs

1. Address Class
2. Answers Class
3. ApexPages Class
4. Approval Class
5. Blob Class
6. Boolean Class
7. BusinessHours Class
8. Cases Class
9. Comparable Interface
10. Continuation Class
11. Cookie Class
12. Crypto Class
13. Custom Settings Methods
14. Database Class.
15. Date Class
16. Datetime Class
17. Decimal Class
18. Double Class
19. EncodingUtil Class
20. Enum Methods
21. Exception Class and Built-In Exceptions
22. FlexQueue Class
23. Http Class
24. HttpCalloutMock Interface
25. HttpRequest Class
26. HttpResponse Class
27. Id Class
28. Ideas Class
29. InstallHandler Interface
30. Integer Class
31. JSON Class
32. JSONGenerator Class
33. JSONParser Class
34. JSONToken Enum
35. Limits Class
36. List Class
37. Location Class
38. Long Class
39. Map Class
40. Matcher Class
41. Math Class
42. Messaging Class
43. MultiStaticResourceCalloutMock Class
44. Network Class
45. PageReference Class
46. Pattern Class
47. Queueable Interface
48. QueueableContext Interface
49. QuickAction Class
50. RemoteObjectController
51. ResetPasswordResult Class
52. RestContext Class
53. RestRequest Class
54. RestResponse Class
55. SandboxPostCopy Interface
56. Schedulable Interface
57. SchedulableContext Interface
58. Schema Class
59. Search Class
60. SelectOption Class
61. Set Class
62. Site Class
63. sObject Class
64. StaticResourceCalloutMock Class
65. String Class
66. System Class
67. Test Class
68. Time Class
69. TimeZone Class
70. Trigger Class
71. Type Class
72. UninstallHandler Interface
73. URL Class
74. UserInfo Class
75. Version Class
76. WebServiceCallout Class
77. WebServiceMock InterfaceXmlStreamReader Class
78. XmlStreamWriter Class

System is Class:

Contains methods for system operations, such as writing debug messages and scheduling jobs.

1. abortJob(jobId)
2. assert(condition, msg)
3. assertEquals(expected, actual, msg)
4. assertNotEquals(expected, actual, msg)
5. currentPageReference()
6. currentTimeMillis()
7. debug(msg)
8. debug(logLevel, msg)
9. enqueueJob(queueableObj)
10. equals(obj1, obj2)
11. getApplicationReadWriteMode()
12. hashCode(obj)
13. isBatch()
14. isFuture()
15. isQueueable()
16. isScheduled()
17. now()
18. process(workItemIds, action, comments, nextApprover)
19. purgeOldAsyncJobs(dt)
20. requestVersion()
21. resetPassword(userId, sendUserEmail)
22. runAs(version)
23. runAs(userSObject)
24. schedule(jobName, cronExpression, schedulableClass)
25. scheduleBatch(batchable, jobName, minutesFromNow)
26. scheduleBatch(batchable, jobName, minutesFromNow, scopeSize)
27. setPassword(userId, password)
28. submit(workItemIds, comments, nextApprover)
29. today()

Always use static .method in trigger contaxt since trigger runs  always in System Contaxt

https://developer.salesforce.com/docs/atlas.en-us.apexcode.meta/apexcode/apex_namespace_System.htm

Trigger Context Variables

1. isExecuting--Returns true if the current context for the Apex code is a trigger, not a Visualforce page, a Web service, or an executeanonymous() API call.
2. isInsert
3. isUpdate
4. isDelete
5. isUndelete--Returns true if this trigger was fired after a record is recovered from the Recycle Bin (that is, after an undelete operation from the Salesforce user interface, Apex, or the API.)
6. isBefore--Returns true if this trigger was fired before any record was saved.
7. isAfter--Returns true if this trigger was fired after all records were saved
8. new--Returns a list of the new versions of the sObject records.Note that this sObject list is only available in insert and update triggers, and the records can only be modified in before triggers.
9. old--Returns a list of the old versions of the sObject records.
   Note that this sObject list is only available in update and delete triggers.
10. newMap--A map of IDs to the new versions of the sObject records.
    Note that this map is only available in after insert, and update triggers.
11. oldMap--A map of IDs to the old versions of the sObject records.Note that this map is only available in update and delete triggers.
12. size--The total number of records in a trigger invocation, both old and new.
13.  Table for defining contaxt variable values "NULL" or "NOT  NULL" 

14. TCV*	Before Insert	After Insert	Before Update	After Update	Before Delete	After Delete	After Undelete
    New	NOT NULL, MODIFIABLE	NOT NULL	NOT NULL,MODIFIABLE	NOT NULL	NULL	NULL	NOT NULL
    Old	NULL	NULL	NOT NULL	NOT NULL	NOT NULL	NOT NULL	NULL
    newMap	NULL	NOT NULL	NOT NULL	NOT NULL	NULL	NULL	NOT NULL
    oldMap	NULL	NULL	NOT NULL	NOT NULL	NOT NULL	NOT NULL	NULL

*TCV->Trigger Context Variable

Events	trigger.old	trigger.oldMap	trigger.new	trigger.newMap
before insert	✘	✘	✔	✘
after insert	✘	✘	✔	✔
before update	✔	✔	✔	✔
after update	✔	✔	✔	✔
before delete	✔	✔	✘	✘
after delete	✔	✔	✘	✘
after undelete	✘	✘	✔	✔

Verified this by trigger refer the link

Open

About Static and instance Method

public class SecondClass
{
int i;
public int sum()
{
int i=5;
return i+this.i;
}
}
---------------------
public class FirstClass
{
public static void main(String args[])
{
SecondClass m=new SecondClass();
m.i=7;
System.out.println("Sum="+m.sum());
}
}

----------------------------

Output:

Sum=12

=============================

public class SecondClass
{
int i;
 public static int sum()
{
int i=5;
return i;
}
}
---------------------
public class FirstClass
{
public static void main(String args[])
{
 SecondClass m=new SecondClass();
 m.i=7;
 System.out.println("Sum="+m.sum());
}
}

static methods are  very far from object instance.that are totaly link to a class.
an another point that static methods can never user non-static members.