Call Apex Class from Custom Button (JAVASCRIPT) in Salesforce

Step 1  :  Lets first create the Apex class

Things to Remember: 

• Class needs to be a Global class 
• and the method you intend to call from the javascript must be a WebService Method

e.g.

Global Class RG_LeadConversionCls {    

webservice static void LeadConvert(Id Leadid)
{       

}


Step 2 : Now to setup the custom Button.

• Goto --> Setup --> Object --> Buttons, links and Actions section
• Click New Button or Link
• Enter the Name of the button
• Behaviour : Execute Javascript
• Content source : On-Click Javascript

{!REQUIRESCRIPT("/soap/ajax/30.0/connection.js")}{!REQUIRESCRIPT("/soap/ajax/30.0/apex.js")}

sforce.apex.execute("RG_LeadConversionCls","LeadConvertId",{Leadid:"{!Lead.Id}"});