代码之家 › 专栏 › 技术社区 › dim

javascript promise finally块内的异步操作

es6-promise javascript

dim · 技术社区 · 8 年前

我正在实现一个函数,该函数返回 Promise . 在它的实现中,我调用另一个函数,它本身返回 承诺 ,在此基础上,我需要对结果进行一点转换。

像这样:

function myDoStuff(params) {
    return actuallyDoStuff(params).then(
        (result) => { return "myTransformation " + result; }
    );
}

现在,我还需要调用一些清理代码,不管这是成功还是失败。我可以加一个 finally 子句到返回的promise,但问题是:在finally子句中我需要做的也是异步的(基本上,另一个函数返回 承诺 再次重申),我需要返回的承诺等待最后定稿完成,然后再定稿。

似乎我不能在 最后 功能(至少在 https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise/finally )

那么,我是否需要从两个方面调用定稿 then 和 catch 或者有什么方法可以使用 最后 构造?

在这两种情况下调用finalization并保留 actuallyDoStuff 导致代码丑陋:

function myDoStuff(params) {
    return actuallyDoStuff(params).then((result) => {
        return doFinalization().then(() => {
            return "myTransformation " + result;
        });   
    }, (err) => {
        return doFinalization().then(() => {
            throw err;
        }), () => {
            throw err;
        });
    });
}

2 回复 | 直到 8 年前

T.J. Crowder 8 年前

finally

function myDoStuff(params) {
    return actuallyDoStuff(params)
        .then(
            (result) => { return "myTransformation " + result; }
        )
        .finally(cleanup);
}

function myDoStuff(params) {
    return actuallyDoStuff(params)
        .then(
            (result) => { return "myTransformation " + result; }
        )
        .finally(() => cleanup().catch(() => {}));
}

// Note this takes only 10ms
function actuallyDoStuff(valueOrError, fail = false) {
  return new Promise((resolve, reject) => {
    setTimeout(fail ? reject : resolve, 10, valueOrError);
  });
}

// Note this takes a full second
function cleanup(fail = false) {
  return new Promise((resolve, reject) => {
    setTimeout(fail ? reject : resolve, 1000, "cleanup done");
  });
}

function myDoStuff(...params) {
    return actuallyDoStuff(...params)
        .then(
            (result) => { return "myTransformation " + result; }
        )
        .finally(cleanup);
}

console.log("start with success");
myDoStuff("success")
  .then(value => console.log("success", value))
  .catch(error => console.log("error", error))
  .finally(() => {
    console.log("Notice how there was a 1,010ms delay, and that the result was from actuallyDoStuff, not cleanup");
    console.log("start with error");
    myDoStuff("error", true)
      .then(value => console.log("success", value))
      .catch(error => console.error("error", error))
      .finally(() => {
        console.log("Notice how there was a 1,010ms delay");
       });
         });

async await

async function myDoStuff(params) {
    try {
        const result = await actuallyDoStuff(params);
        return return "myTransformation " + result;
    } finally {
        await cleanup(); // Allows errors from cleanup
    }
}

async function myDoStuff(params) {
    try {
        const result = await actuallyDoStuff(params);
        return "myTransformation " + result;
    } finally {
        await cleanup().catch(() => {}); // Suppresses errors from cleanup
    }
}

try catch

async function myDoStuff(params) {
    try {
        const result = await actuallyDoStuff(params);
        return "myTransformation " + result;
    } finally {
        try {
            await cleanup()
        } catch (e) { // As of ES2019, you could leave the `(e)` off
                      // That's already at Stage 4
        }
    }
}

ponury-kostek 8 年前

如果要返回原始结果 actuallyDoStuff 之后 doFinalization

function myDoStuff(params) {
	return actuallyDoStuff(params).then((result) => {
		return doFinalization().then(() => {
			return "myTransformation " + result;
		}).finally(doFinalization);
	});
}

function doFinalization(result) {
	console.log("Finalizing"); // It can be async or not
	return Promise.resolve("finalized").then(() => {
		// return original resolution of actuallyDoStuff
		return result;
	});
}

function actuallyDoStuff(params) {
	console.log("Doing stuff");
	return params ? Promise.resolve("ok") : Promise.reject("failed");
}

myDoStuff(true).then(res => console.log("Result", res)).catch(err => console.error("Error", err));
myDoStuff(false).then(res => console.log("Result", res)).catch(err => console.error("Error", err));