Event listener

An event listener is JavaScript code that runs when something happens on a page, such as a click, a key press, or a touch. Pages register listeners for the events they care about; most interactive behavior on the modern web is built this way.

An event listener that does too much work directly on the main thread - heavy calculations, large DOM updates - is a common cause of a page feeling unresponsive to taps and clicks, which shows up as poor INP.

Learn more

• EventTarget: addEventListener() method - MDN's reference documentation
• Main thread
• INP