The Qlik Extension API consists of methods and properties to create custom visualization extensions in Qlik. This is a very powerful API, as it allows you to efficiently embed any JavaScript code, visualizations, or custom components into Qlik Sense and, using the property panel, to configure certain aspects of that extension.
Basic examples of use can be found as follows, which can help you get a better idea of how the Extension API can be leveraged within Qlik Sense.