Long Task

A long task is any piece of JavaScript code that monopolizes the Main Thread for a prolonged period (typically over 50 milliseconds), preventing it from responding to user input. While a long task is running, the browser cannot react to clicks or taps, making the page feel frozen and unresponsive. Long tasks are a primary cause of a poor Interaction to Next Paint (INP) score. The most effective way to optimize them is to break them into a series of smaller tasks, yielding control back to the main thread between each one.