Difference between Action support and Action function

Action function

Actionfunction is a function that can be called by any component via onclick, ondbclick, onblur event of that component. In Action function we invoke AJAX using Java script. It Provides support for invoking controller action methods directly from JavaScript code using an AJAX request Used when we need to perform similar action on various events. Even though you can use it in place of actionSupport as well where only event is related to only one control.

Action function may be commonly used from different place on page while action support may only be used for particular single apex component.

Example:

<!-- Page: -->
<apex:page controller="exampleCon">
<apex:form>
<!-- Define the JavaScript function sayHello-->
<apex:actionFunction name="sayHello" action="{!sayHello}" rerender="out"
status="myStatus"/>
</apex:form>
<apex:outputPanel id="out">
<apex:outputText value="Hello "/>
<apex:actionStatus startText="requesting..." id="myStatus">
<apex:facet name="stop">{!username}</apex:facet>
</apex:actionStatus>
</apex:outputPanel>
<!-- Call the sayHello JavaScript function using a script element-->
<script>window.setTimeout(sayHello,2000)</script>
<p><apex:outputText value="Clicked? {!state}" id="showstate" /></p>
<!-- Add the onclick event listener to a panel. When clicked, the panel triggers
the methodOneInJavascript actionFunction with a param -->
<apex:outputPanel onclick="methodOneInJavascript('Yes!')" styleClass="btn">
Click Me
</apex:outputPanel>
<apex:form>
<apex:actionFunction action="{!methodOne}" name="methodOneInJavascript"
rerender="showstate">
<apex:param name="firstParam" assignTo="{!state}" value="" />
</apex:actionFunction>
</apex:form>
</apex:page>

/*** Controller ***/
public class exampleCon {
String uname;
public String getUsername() {
return uname;
}
public PageReference sayHello() {
uname = UserInfo.getName();
return null;
}
public void setState(String n) {
state = n;
}
public String getState() {
return state;
}
public PageReference methodOne() {
return null;
}
private String state = 'no';
}

Action Support:

ActionSupport is added to a particular component like button or outputtext and the event is controlled by the actionsupport not the component thus actionsupport help enhance the compononment itself by being part of the component itself. In Action support we may directly invoke method from controller.






A component that adds AJAX support to another component, allowing the component to be refreshed asynchronously by the server when a particular event occurs, such as a button click or mouseover. Used when we want to perform an action on a particular event of any control like onchange of any text box or picklist.





Example:










<apex:page controller="exampleCon">
<apex:form>
<apex:outputpanel id="counter">
<apex:outputText value="Click Me!: {!count}"/>
<apex:actionSupport event="onclick"
action="{!incrementCounter}"
rerender="counter" status="counterStatus"/>
</apex:outputpanel>
<apex:actionStatus id="counterStatus"
startText=" (incrementing...)"
stopText=" (done)"/>
</apex:form>
</apex:page>


/*** Controller: ***/
public class exampleCon {
Integer count = 0;
public PageReference incrementCounter() {
count++;
return null;
}
public Integer getCount() {
return count;
}
}




Please check below below blog for more information
http://www.cloudforce4u.com/2013/06/difference-between-action-support-and.html