^29 event cycle model

1、 All code categories ：

- Initialize the execution code ( Synchronization code )： Include binding DOM Event monitoring 、 Set the timer 、 happen ajax Requested code

- Callback execution code ( Asynchronous code )： Handle callback logic

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2、JS The basic flow of engine execution code

Initialization code => callback code

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3、 Two important components of the model

                Event management module

                The callback queue

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4、 The operation process of the model

- Execute initialization code , Give the event callback function to the corresponding module for management

- When the event occurs , The management module will add the callback function and its data to the callback queue

- Only after the initialization code is executed ( It may take some time ), Will traverse the callback function execution in the callback queue

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5、 Important concepts  

                (1、 Execution stack ： All code is executed in this space )

                (2、 Browser kernel ：JS Engine modules ( The main thread )、 Other modules ( Lord / Sub thread ))

                (3、 Task queue )

                (4、 Message queue )

                (5、 Event queue )

                    3、4、5 In the same callback queue

                (6、 Event polling ： Take the callback function from the task queue and put it into the execution stack )

                (7、 Event driven model ： Upper figure )

                (8、 Request response model ： browser 、 Transfer data between servers )

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