将参数的顺序交换为"then"与Bluebird/NodeJS的承诺 [英] Swap order of arguments to "then" with Bluebird / NodeJS Promises

问题描述

我有一个从服务器异步获取值的函数:

I have a function which asynchronously grabs a value from a server:

var request = require('request');
Promise.promisifyAll(request);
function getValue(){
    return request.getAsync('http://www.google.com')
        .then(function(resp){ return resp.body; })
        .catch(function(err){ thow err; });
}

我要使用此值并将其转储到文件中

I want to take this value and dump it to a file:

var fs = require('fs');
Promise.promisifyAll(fs);
getValue().then(fs.writeFileAsync, "file.html");

问题是fs.writeFileAsync希望参数1是文件，而参数2是数据，但是getValue()返回数据.这是错误的说法:

The problem is that fs.writeFileAsync expects parameter one to be the file and parameter two to be the data, but getValue() returns the data. This is error'ing out saying:

Unhandled rejection Error: ENAMETOOLONG: name too long, open '<html....'
    at Error (native)

我现在可以通过编写一个辅助函数来交换参数来规避这一点:

I could circumvent this for now by writing a helper function to swap the parameters:

function myWriteFile(data, fileName) {
    return fs.writeFileAsync(fileName, data);
}

尽管有可能在不编写首选的辅助函数的情况下解决此问题，因为我希望会出现很多类似的问题，并且不想将50个辅助函数弄乱我的代码.我还觉得从诺言将数据传递到writeFile可能是一个非常常见的用例.

Although if it's possible to fix this without writing a helper function that would be preferred, as I expect a lot of similar issues to arise and don't want to clutter my code with 50 helper functions. I also feel like passing data to writeFile from a promise is probably a very common use case.

推荐答案

.then()函数的第二个参数是错误回调，而不是参数.您的代码根本不起作用.

The second parameter to the .then() function is an error callback, not a parameter. Your code doesn't work at all.

相反，您可以使用.bind预先绑定参数:

Instead, you can use .bind to pre-bind a parameter:

getValue().then(fs.writeFileAsync.bind(null, "file.html"));

请注意，.bind()的第一个参数是this参数，这无关紧要.

Note that the first parameter to .bind() is the this parameter, which doesn't matter.

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