Question

以下代码返回：

output.isPending?: true
output.isRejected?: false
output.isFulfilled?: false

为什么呢？我期待output.isRejected成为true。

<html>

<head>
    <script src="http://cdnjs.cloudflare.com/ajax/libs/q.js/0.9.7/q.js"></script>
    <script src="http://jasmine.github.io/2.3/lib/jasmine.js"></script>
</head>

<body>
</body>
<script>
var output, bar;

bar = {
    doSomethingAsync: function() {
        var d = Q.defer();
        d.resolve('result');
        return d.promise;
    }
};

function Foo(bar) {
    this._bar = bar;

    this.go = function() {
        var deferred = Q.defer();
        this._bar.doSomethingAsync()
            .then(onSuccess.bind(this, deferred));

        return deferred.promise;
    }
};

function onSuccess(deferred, result) {
    deferred.reject();
}

output = new Foo(bar).go()
    .finally(function() {
        console.log('output.isPending?:', output.isPending());
        console.log('output.isRejected?:', output.isRejected());
        console.log('output.isFulfilled?:', output.isFulfilled());
    });
</script>

</html>

Answer 1

因为output不是new Foo(bar).go()。它会被分配.finally()调用的结果，并且在finally回调完成后仍无法解析。

这将按预期工作：

var output = new Foo(bar).go();
output.finally(function() {
    console.log('output.isPending?:', output.isPending());
    console.log('output.isRejected?:', output.isRejected());
    console.log('output.isFulfilled?:', output.isFulfilled());
});

Answer 2

我立即纠正了一个微不足道的延迟函数，即使是对于承诺无视的API也是不必要的。我可以确保始终调用resolve或reject，但是在承诺本身被立即返回之后。这是一个例子：

var somePromise = function(path) {
    var deferred = q.defer();

    asyncFunction.request(path, function(result) {
        if (result.error === 0 && result.json !== null) {
            deferred.resolve(result);
        } else {
            deferred.reject(result || {error: -1, message: "bad things happened"});
        }
    });

    return deferred.promise;
};

exports.someCall = function(req,res) {
    somePromise('path')
        .then(function (result) {
            ... do action ...
        }).catch(function (error) {
            ... handle error ...
        }); 
};

为什么承诺仍未决定？

2 个答案: