Promise.resolve和新Promise(resolve)是否可互换 [英] Are Promise.resolve and new Promise(resolve) interchangeable

问题描述

我认为 Promise.resolve 和 new Promise(resolve)是可以互换的.

I think Promise.resolve and new Promise(resolve) are interchangeable.

考虑一下:

A.

new RSVP.Promise(function (resolve, reject) {
    resolve();
}).then(function () {
    return new RSVP.Promise(function (resolve) {
        resolve("HI")
    });
}).then(function (result) {
    console.log(result);
});

B.

new RSVP.Promise(function (resolve, reject) {
    resolve();
}).then(function () {
    return RSVP.resolve("HI");
}).then(function (result) {
    console.log(result);
});

我都期望打印两个"HI".

Both print "HI" as I expected.

所以我认为如果我不需要拒绝"任何东西.为了简单起见，我只能编写 RSVP.resolve(); .

So I think if I don't need to "reject" anything. I can just write RSVP.resolve(); for simplicity.

但请考虑以下示例:

new RSVP.Promise(function (resolve, reject) {
    resolve();
}).then(function () {
    return new RSVP.Promise(function (resolve, reject) {
        setTimeout(function () {
            resolve("HI")
        }, 3000);
    });
}).then(function (result) {
    console.log(result);
});

如何使用 RSVP.resolve(); 进行替换?我尝试了例如:

How can I use RSVP.resolve(); to replace? I tried for example:

new RSVP.Promise(function (resolve, reject) {
    resolve();
}).then(function () {
    return setTimeout(function () {
        return new RSVP.resolve("HI");
    }, 3000);
}).then(function (result) {
    console.log(result);
});

这将打印其他内容，而不是"HI".因此可以使用RSVP.resolve();这里?这两个可以互换吗?

This prints something else instead of "HI". So is it possible to use RSVP.resolve(); here? Are these two interchangeable?

推荐答案

首要的

我认为Promise.resolve和新的Promise(resolve)是可以互换的.

I think Promise.resolve and new Promise(resolve) are interchangeable.

不. Promise.resolve 将创建一个已解决的承诺，而 new Promise(resolve)将创建一个既未解决也不拒绝的承诺.

Nope. Promise.resolve will create a promise which is already resolved, whereas new Promise(resolve) creates a promise which is neither resolved nor rejected.

在最后一个示例中，

return setTimeout(function () {
    return new RSVP.resolve("HI");
}, 3000);

表示您要返回的是 setTimeout 函数的结果，而不是诺言对象.因此，当前的 then 处理程序将返回解析的promise，其结果为 setTimeout .这就是为什么您看到一个奇怪的物体.

means that, you are returning the result of setTimeout function, not a promise object. So, the current then handler will return a resolved promise with the result of setTimeout. That is why you are seeing a weird object.

在您的特定情况下，您想在解决承诺之前引入延迟. Promise.resolve 是不可能的.问题中显示的倒数第二种方法是解决方法.

In your particular case, you want to introduce a delay before resolving the promise. It is not possible with Promise.resolve. The penultimate method you have shown in the question, is the way to go.

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