更正 node.js 中的异步函数导出

这实际上与异步函数没有任何关系.如果你想在内部调用一个函数and，导出它，定义它first，然后导出它.

async function doStuff() {
  // ...
}
// doStuff is defined inside the module so we can call it wherever we want

// Export it to make it available outside
module.exports.doStuff = doStuff;

解释您try 的问题:

module.exports.PrintNearestStore = async function PrintNearestStore(session, lat, lon) {
...
}

这不会在模块中定义函数.函数定义是一个函数expression.函数表达式的名称仅在函数本身内部创建变量.更简单的例子:

var foo = function bar() {
  console.log(typeof bar); // 'function' - works
};
foo();
console.log(typeof foo); // 'function' - works
console.log(typeof bar); // 'undefined' - there is no such variable `bar`

另见第Named function expressions demystified页.如果你在任何地方都提到module.exports.PrintNearestStore，你当然可以提到这个函数.

module.exports.PrintNearestStore = PrintNearestStore;

var PrintNearestStore = async function(session, lat, lon) {

}

好的.问题是，当您将PrintNearestStore指定给module.exports.PrintNearestStore时，它的值是undefined.执行顺序如下:

var PrintNearestStore; // `undefined` by default
// still `undefined`, hence `module.exports.PrintNearestStore` is `undefined`
module.exports.PrintNearestStore = PrintNearestStore;

PrintNearestStore = async function(session, lat, lon) {}
// now has a function as value, but it's too late

更简单的例子:

var foo = bar;
console.log(foo, bar); // logs `undefined`, `undefined` because `bar` is `undefined`
var bar = 21;
console.log(foo, bar); // logs `undefined`, `21`

如果您更改了顺序，它将按预期工作.

module.exports.PrintNearestStore = async function(session, lat, lon) {
    await PrintNearestStore(session, lat, lon);
}

var PrintNearestStore = async function(session, lat, lon) {
...
}

这是因为分配给module.exports.PrintNearestStoreis executedPrintNearestStore的函数将函数作为其值.

更简单的例子:

var foo = function() {
  console.log(bar);
};
foo(); // logs `undefined`
var bar = 21;
foo(); // logs `21`