How to use the js async function
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The async function is the syntax sugar of the Generator function. The async function simply replaces the asterisk (*) of the Generator function with async and yield with await, that's all.
The improvement point of async function to Generator function
The built-in executor does not need to call next () like the Generator function to make the function execute.
Better semantics
The promise object is returned
The async function returns a promise object
The async function returns a Promise object. The value returned by the return statement inside the async function becomes the parameter of the callback function of the then method. An error is thrown inside the async function, which causes the returned Promise object to become reject. The error object thrown will be received by the callback function of the catch method
See the following example:
LettestAsync=asyncfunction () {
/ / thrownewError ('throw an error ~')
Reject ()
}
TestAsync () .then (resolve= > {
Console.log (`resolve:$ {resolve} `)
}, reject= > {
Console.log (`reject:$ {reject} `); / / the callback function in which the status changes to reject will be executed. If there is no callback function here, catch will capture it. This is the thing of promise.
}) .catch (err= > {
Console.log (`err:$ {err} `)
})
If any Promise object following an await statement changes to the reject state, the entire async function interrupts execution.
Asyncfunctionf () {
AwaitPromise.reject ('error')
AwaitPromise.resolve ('helloworld'); / / will not be executed
}
/ / the promise statement on the second line will not be executed
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