node.js - 如何将异步 Node 函数转变为 Promise

Question

我有一个异步函数，我想把它变成一个 promise

    var myAsyncFunction = function(err, result) {
        if (err) 
            console.log("We got an error");


        console.log("Success");
    };

    myAsyncFunction().then(function () { console.log("promise is working"); });

我收到 TypeError: Cannot call method 'then' of undefined.

这段代码有什么问题？

Answer 1

有various ways在问题中:

Q.nfcall(myAsyncFunction, arg1, arg2);
Q.nfapply(myAsyncFunction, [arg1, arg2]);

// Work with rusable wrapper
var myAsyncPromiseFunction = Q.denodeify(myAsyncFunction);
myAsyncPromiseFunction(arg1, arg2);

在 Deferred实现:

var myAsyncPromiseFunction = deferred.promisify(myAsyncFunction);
myAsyncPromiseFunction(arg1, arg2);

一个显着的区别:由 Deferred 生成的包装器另外自动解析作为参数传递的 promise ，因此您可以执行以下操作:

var readFile = deferred.promisify(fs.readFile);
var writeFile = deferred.promisify(fs.writeFile);

// Copy file
writeFile('filename.copy.txt', readFile('filename.txt'));