Javascript 节点在继续之前等待异步功能
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Node wait for async function before continue
提问by user2520969
I have a node application that use some async functions.
我有一个使用一些异步函数的节点应用程序。
How can i do for waiting the asynchronous function to complete before proceeding with the rest of the application flow?
在继续应用程序流程的其余部分之前，我该如何等待异步函数完成？
Below there is a simple example.
下面有一个简单的例子。
var a = 0;
var b = 1;
a = a + b;
// this async function requires at least 30 sec
myAsyncFunction({}, function(data, err) {
a = 5;
});
// TODO wait for async function
console.log(a); // it must be 5 and not 1
return a;
In the example, the element "a" to return must be 5 and not 1. It is equal to 1 if the application does not wait the async function.
在示例中，a要返回的元素“ ”必须是 5 而不是 1。如果应用程序不等待异步函数，则它等于 1。
Thanks
谢谢
回答by Ozgur
?Using callback mechanism:
?使用回调机制：
function operation(callback) {
var a = 0;
var b = 1;
a = a + b;
a = 5;
// may be a heavy db call or http request?
// do not return any data, use callback mechanism
callback(a)
}
operation(function(a /* a is passed using callback */) {
console.log(a); // a is 5
})
?Using async await
?使用异步等待
async function operation() {
return new Promise(function(resolve, reject) {
var a = 0;
var b = 1;
a = a + b;
a = 5;
// may be a heavy db call or http request?
resolve(a) // successfully fill promise
})
}
async function app() {
var a = await operation() // a is 5
}
app()
