Promise async/await

Promise Receive a function to do , This function receives resolve,reject These two functions are used as arguments

Promise Give asynchronous operations a state ：

EH I haven't started the operation yet , The status is pending

The asynchronous operation was successfully executed resolve function , The status is fullfilled

Asynchronous operation failed to execute reject function , The status is rejected

To facilitate chained calls , He will return to a new promise Object and wrap the results of the asynchronous operation

.then Method passes two callback functions as parameters

The first function is used to execute a successful callback , The second function is used to execute the failed callback

.catch It is triggered when an error occurs at any stage , And the back then Will not proceed with

.finally Execute after the chain call , Whether the execution fails or not

async/await Is based on promise The grammar sugar of

async Mark a function as asynchronous , Can be used in await Call other asynchronous functions ,await Will be in promise After completion, return to the final result directly