1. The three stages of dom event flow

(1) event capture stage (2) In the target stage (3) event bubble stage

When an event is triggered, it propagates between child and parent elements in three stages: 1. Capture stage: The capture stage is propagated successively from the Window object down to the target node. The capture phase does not respond to any events. 2. Target phase: Events are triggered at the target node, which is target phase 3. Bubble phase: The bubble phase is propagated from the target phase up to the Window object. 【 Event broker is to bind the events that the inner elements need to respond to to the outer elements by the mechanism of event bubble. 】