This allows for the end-user to update parts of the Web screen and not to have to wait for the response, while keeping the state of the page.
Think of filling a form with validations. With Ajax, validations of inputs are asynchronously requested to the server as the end-user fills them in. Once there's a response, it is rendered next to the corresponding field while the user goes on filling.
This delivers a better experience to end-users, with validations as they go and no waiting time for those validations.
In OutSystems Platform, there is a set of built-in tools that allow you to quickly implement Ajax techniques to improve the end-user experience in each situation.
To refresh a widgets that are part of the Web Screen, simply give a name to those widgets and use the Ajax Refresh tool to in screens actions.
In those actions change their Method property to Ajax Submit.
Learn more About the Ajax Refresh Tool.
There are some widgets in Service Studio that have built-in Ajax capabilities.
In these widgets, you may set a screen action that is executed as an Ajax request when an event occurs in the widget.
Learn more about Widgets with Ajax Capabilities.
There are some System actions in Service Studio that have built-in Ajax capabilities.
They allow you manipulate a single row in list widgets without having to refresh the whole list.
Learn more about System Actions with Ajax Capabilities.
Check the How to Design Screens with Ajax sample at OutSystems Forge.
Widgets with Ajax Capabilities | System Actions with Ajax Capabilities