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2023-05-07 08:00:05

如何将现有回调API转换为promise？

我想使用promise，但我有一个回调API，格式如下：

1.DOM加载或其他一次性事件：

window.onload; // set to callback
...
window.onload = function() {

};

2.普通回调：

function request(onChangeHandler) {
    ...
}
request(function() {
    // change happened
    ...
});

3.节点样式回调（“nodeback”）：

function getStuff(dat, callback) {
    ...
}
getStuff("dataParam", function(err, data) {
    ...
})

4.具有节点样式回调的整个库：

API;
API.one(function(err, data) {
    API.two(function(err, data2) {
        API.three(function(err, data3) {
            ...
        });
    });
});

我如何在promise中使用API，如何“promise”它？

当前回答

在内置promise和异步的节点v7.6+下：

// promisify.js
let promisify = fn => (...args) =>
    new Promise((resolve, reject) =>
        fn(...args, (err, result) => {
            if (err) return reject(err);
            return resolve(result);
        })
    );

module.exports = promisify;

如何使用：

let readdir = require('fs').readdir;
let promisify = require('./promisify');
let readdirP = promisify(readdir);

async function myAsyncFn(path) {
    let entries = await readdirP(path);
    return entries;
}
2017-04-12 16:48:09

其他回答

也许已经回答了，但我通常是这样做的：

// given you've defined this `Future` fn somewhere:
const Future = fn => {return new Promise((r,t) => fn(r,t))}

// define an eventFn that takes a promise `resolver`
const eventFn = resolve => {
  // do event related closure actions here. When finally done, call `resolve()`
  something.oneventfired = e => {resolve(e)}
}

// invoke eventFn in an `async` workflowFn using `Future`
// to obtain a `promise` wrapper
const workflowFn = async () => {await Future(eventFn)}

特别是对于indexedDb事件包装器之类的东西，以简化使用。

或者你可能会发现未来的这种变化更具普遍性

class PromiseEx extends Promise {
  resolve(v,...a) {
    this.settled = true; this.settledValue = v;
    return(this.resolve_(v,...a))
  }
  reject(v,...a) {
    this.settled = false; this.settledValue = v;
    return(this.reject_(v,...a))
  }
  static Future(fn,...args) {
    let r,t,ft = new PromiseEx((r_,t_) => {r=r_;t=t_})
    ft.resolve_ = r; ft.reject_ = t; fn(ft,...args);
    return(ft)
  }
}
2020-12-27 03:56:38

您可以在NodeJS中使用JavaScript本机承诺。

My Cloud 9代码链接：https://ide.c9.io/adx2803/native-promises-in-node

/**
* Created by dixit-lab on 20/6/16.
*/

var express = require('express');
var request = require('request');   //Simplified HTTP request client.


var app = express();

function promisify(url) {
    return new Promise(function (resolve, reject) {
        request.get(url, function (error, response, body) {
            if (!error && response.statusCode == 200) {
                resolve(body);
            }
            else {
                reject(error);
            }
        })
    });
}

//get all the albums of a user who have posted post 100
app.get('/listAlbums', function (req, res) {
    //get the post with post id 100
    promisify('http://jsonplaceholder.typicode.com/posts/100').then(function (result) {
        var obj = JSON.parse(result);
        return promisify('http://jsonplaceholder.typicode.com/users/' + obj.userId + '/albums')
    })
    .catch(function (e) {
        console.log(e);
    })
    .then(function (result) {
        res.end(result);
    })
})

var server = app.listen(8081, function () {
    var host = server.address().address
    var port = server.address().port

    console.log("Example app listening at http://%s:%s", host, port)
})

//run webservice on browser : http://localhost:8081/listAlbums
2016-06-20 13:38:56

在Node.js 8.0.0的候选版本中，有一个新的实用程序util.profisify（我已经写过util.proficify），它封装了promising任何函数的能力。

它与其他答案中建议的方法没有太大不同，但具有作为核心方法而不需要额外依赖性的优点。

const fs = require('fs');
const util = require('util');

const readFile = util.promisify(fs.readFile);

然后有一个readFile方法，它返回一个本机Promise。

readFile('./notes.txt')
  .then(txt => console.log(txt))
  .catch(...);
2017-05-16 05:35:57

死灵一点，这个链接可能有用。。。。

太长，读不下去了看看这个答案末尾的代码片段示例

编写/转换可调用的函数

cb（错误，结果）或新Promise（…）格式

promiseToCB转换并导出先前编码为返回promise的现有函数cbToPromise转换并导出一个先前编码为调用最后一个参数的现有函数（error，result）如果包装函数提供了多个结果，则结果将是一个结果数组例如cb（undefined，path，stat）--->解析（[path，stat]）/cb（undefine，[path，stat]）asPromise允许您编写一个新函数以返回promise，但它可以以任何方式调用asCallback允许您编写一个新函数来调用cb（err，result），但它可以通过任何方式调用

示例函数

每个样本取2个参数，并基于随机数解决/拒绝/错误。

arg2也可以用于强制通过或失败。（查找“-通过”或“-失败”）。

包装现有函数

将函数导出到当前的“this”（或使用promiseToCB（函数myFunc（）｛｝，newThis）；）


    promiseToCB(function sampleFunc1(arg1,arg2) {
        console.log("deciding:",arg1,arg2);
        return new Promise(function(resolve,reject){
       
           const timer = setTimeout(function(){reject([arg1,arg2,"ouch"].join("-"));},5000);
           
           setTimeout(function(){
               if (arg2.endsWith("-pass") || (!arg2.endsWith("-fail") && Math.random()<0.5)) {
    
                   console.log("complete:",arg1,arg2);
                   clearTimeout(timer);
                   resolve([arg1,arg2,"all good"].join("-"));
               }
           },2000);
        
        });
    });
    
    cbToPromise('sampleFunc2',function someOtherName(arg1,arg2,cb) {
       console.log("deciding:",arg1,arg2);
       const timer = setTimeout(function(){cb([arg1,arg2,"ouch"].join("-"));},5000);
       
       setTimeout(function(){
           if (arg2.endsWith("-pass") || (!arg2.endsWith("-fail") && Math.random()<0.5)) {
               console.log("complete:",arg1,arg2);
               clearTimeout(timer);
               cb(undefined,[arg1,arg2,"all good"].join("-"));
           }
       },2000);
        
    },local);

或者编写嵌入包装器的新函数。

     function sampleFunc3(arg1,arg2) {return asPromise(arguments,function(resolve,reject){
       console.log("deciding:",arg1,arg2);
       const timer = setTimeout(function(){reject([arg1,arg2,"ouch"].join("-"));},5000);
       
       setTimeout(function(){
           if (arg2.endsWith("-pass") || (!arg2.endsWith("-fail") && Math.random()<0.5)) {
               console.log("complete:",arg1,arg2);
               clearTimeout(timer);
               resolve([arg1,arg2,"all good"].join("-"));
           }
       },2000);
        
    });}
    
    function sampleFunc4(arg1,arg2) {return asCallback(arguments,function(cb){
       console.log("deciding:",arg1,arg2);
       const timer = setTimeout(function(){cb([arg1,arg2,"ouch"].join("-"));},5000);
       
       setTimeout(function(){
           if (arg2.endsWith("-pass") || (!arg2.endsWith("-fail") && Math.random()<0.5)) {
               console.log("complete:",arg1,arg2);
               clearTimeout(timer);
               cb(undefined,[arg1,arg2,"all good"].join("-"));
           }
       },2000);
        
    });}

测试上述功能的scipt


    const local = {}; 
    promiseToCB(function sampleFunc1(arg1,arg2) {
        console.log("deciding:",arg1,arg2);
        return new Promise(function(resolve,reject){
       
           const timer = setTimeout(function(){reject([arg1,arg2,"ouch"].join("-"));},5000);
           
           setTimeout(function(){
               if (arg2.endsWith("-pass") || (!arg2.endsWith("-fail") && Math.random()<0.5)) {
    
                   console.log("complete:",arg1,arg2);
                   clearTimeout(timer);
                   resolve([arg1,arg2,"all good"].join("-"));
               }
           },2000);
        
        });
    });
    
    cbToPromise('sampleFunc2',function someOtherName(arg1,arg2,cb) {
       console.log("deciding:",arg1,arg2);
       const timer = setTimeout(function(){cb([arg1,arg2,"ouch"].join("-"));},5000);
       
       setTimeout(function(){
           if (arg2.endsWith("-pass") || (!arg2.endsWith("-fail") && Math.random()<0.5)) {
               console.log("complete:",arg1,arg2);
               clearTimeout(timer);
               cb(undefined,[arg1,arg2,"all good"].join("-"));
           }
       },2000);
        
    },local);
    
    function sampleFunc3(arg1,arg2) {return asPromise(arguments,function(resolve,reject){
       console.log("deciding:",arg1,arg2);
       const timer = setTimeout(function(){reject([arg1,arg2,"ouch"].join("-"));},5000);
       
       setTimeout(function(){
           if (arg2.endsWith("-pass") || (!arg2.endsWith("-fail") && Math.random()<0.5)) {
               console.log("complete:",arg1,arg2);
               clearTimeout(timer);
               resolve([arg1,arg2,"all good"].join("-"));
           }
       },2000);
        
    });}
    
    function sampleFunc4(arg1,arg2) {return asCallback(arguments,function(cb){
       console.log("deciding:",arg1,arg2);
       const timer = setTimeout(function(){cb([arg1,arg2,"ouch"].join("-"));},5000);
       
       setTimeout(function(){
           if (arg2.endsWith("-pass") || (!arg2.endsWith("-fail") && Math.random()<0.5)) {
               console.log("complete:",arg1,arg2);
               clearTimeout(timer);
               cb(undefined,[arg1,arg2,"all good"].join("-"));
           }
       },2000);
        
    });}
    
    const log=console.log.bind(console),info=console.info.bind(console),error=console.error.bind(console);
    
    sampleFunc1("sample1","promise").then (log).catch(error);
    local.sampleFunc2("sample2","promise").then (log).catch(error);
    sampleFunc3("sample3","promise").then (log).catch(error);
    sampleFunc4("sample4","promise").then (log).catch(error);

    sampleFunc1("sample1","callback",info);
    local.sampleFunc2("sample2","callback",info);
    sampleFunc3("sample3","callback",info);
    sampleFunc4("sample4","callback",info);
    
    sampleFunc1("sample1","promise-pass").then (log).catch(error);
    local.sampleFunc2("sample2","promise-pass").then (log).catch(error);
    sampleFunc3("sample3","promise-pass").then (log).catch(error);
    sampleFunc4("sample4","promise-pass").then (log).catch(error);

    sampleFunc1("sample1","callback-pass",info);
    local.sampleFunc2("sample2","callback-pass",info);
    sampleFunc3("sample3","callback-pass",info);
    sampleFunc4("sample4","callback-pass",info);
    
    
    sampleFunc1("sample1","promise-fail").then (log).catch(error);
    local.sampleFunc2("sample2","promise-fail").then (log).catch(error);
    sampleFunc3("sample3","promise-fail").then (log).catch(error);
    sampleFunc4("sample4","promise-fail").then (log).catch(error);
    
    sampleFunc1("sample1","callback-fail",info);
    local.sampleFunc2("sample2","callback-fail",info);
    sampleFunc3("sample3","callback-fail",info);
    sampleFunc4("sample4","callback-fail",info);

var cpArgs=Array.prototype.slice.call.bind（Array.proto原型.slice）；函数promiseToCB（nm，fn，THIS）{如果（nm类型==='功能'）{这=fn；fn=纳米；nm=fn.name；}此=此||此；const func=函数（）{let args=cpArgs（参数）；if（参数类型[args.length-1]=='函数'）{const cb=args.pop（）；return fn.apply（THIS，args）.then（函数（r）{cb（未定义，r）；}).捕获（cb）；}其他{return fn.apply（THIS，args）；}};Object.defineProperty（func，'name'，{value:nm，enumerable:false，可配置：true}）；如果（此[nm]）删除此[nm]；Object.defineProperty（THIS，nm，｛value:func，enumerable:false，可配置：true｝）；返回函数；}函数cbToPromise（nm，fn，THIS）{如果（nm类型==='功能'）{这=fn；fn=纳米；nm=fn.name；}此=此||此；const func=函数（）{let args=cpArgs（参数）；if（参数类型[args.length-1]=='函数'）{return fn.apply（THIS，args）；}其他{return new Promise（函数（解析，拒绝）{args.push（函数（错误，结果）{if（error）返回reject（err）；if（arguments.length==2）{返回解析（result）；}返回解析（cpArgs（arguments，1））；});fn.apply（此，参数）；});}};Object.defineProperty（func，'name'，{value:nm，enumerable:false，可配置：true}）；如果（此[nm]）删除此[nm]；Object.defineProperty（THIS，nm，｛value:func，enumerable:false，可配置：true｝）；返回函数；}函数作为Promise（args，解析器，no_err）{常量cb=参数[args.length-1]，promise=新promise（解析器）；return（cb类型=='函数'）？promise.then（函数（结果）｛return cb（no-err，结果）｝）.catch（cb）：promise；}函数作为回调（args，wrap，no_err）{常量cb=参数[args.length-1]，promise=新promise（函数解析器（resolve，reject）{返回换行（函数（错误，结果）{if（error）返回reject（err）；解决（结果）；});});return（cb类型=='函数'）？promise.then（函数（结果）｛return cb（no-err，结果）｝）.catch（cb）：promise；}函数cbPromiseTest（）{/*全局样本Func1，样本Func2*/常量local={}；promiseToCB（函数sampleFunc1（arg1，arg2）{console.log（“决定：”，arg1，arg2）；return new Promise（函数（解析，拒绝）{const timer=setTimeout（函数（）｛reject（[arg1，arg2，“ouch”].jjoin（“-”）；｝，5000）；setTimeout（函数）{if（arg2.endsWith（“-pass”）||（！arg2.ends With（”-ffail“）&&Math.random（）<0.5））{console.log（“完成：”，arg1，arg2）；clearTimeout（计时器）；解析（[arg1，arg2，“一切正常”].join（“-”））；}},2000);});});cbToPromise（'sampleFunc2'，函数someOtherName（arg1，arg2，cb）{console.log（“决定：”，arg1，arg2）；const timer=setTimeout（函数）｛cb（[arg1，arg2，“ouch”].jjoin（“-”）；｝，5000）；setTimeout（函数）{if（arg2.endsWith（“-pass”）||（！arg2.ends With（”-ffail“）&&Math.random（）<0.5））{console.log（“完成：”，arg1，arg2）；clearTimeout（计时器）；cb（未定义，[arg1，arg2，“all good”]。join（“-”））；}},2000);}，本地）；函数sampleFunc3（arg1，arg2）｛return asPromise（参数，函数（解析，拒绝）{console.log（“决定：”，arg1，arg2）；const timer=setTimeout（函数（）｛reject（[arg1，arg2，“ouch”].jjoin（“-”）；｝，5000）；setTimeout（函数）{if（arg2.endsWith（“-pass”）||（！arg2.ends With（”-ffail“）&&Math.random（）<0.5））{console.log（“完成：”，arg1，arg2）；clearTimeout（计时器）；解析（[arg1，arg2，“一切正常”].join（“-”））；}},2000);});}函数sampleFunc4（arg1，arg2）｛return asCallback（参数，函数（cb）{console.log（“决定：”，arg1，arg2）；const timer=setTimeout（函数）｛cb（[arg1，arg2，“ouch”].jjoin（“-”）；｝，5000）；setTimeout（函数）{if（arg2.endsWith（“-pass”）||（！arg2.ends With（”-ffail“）&&Math.random（）<0.5））{console.log（“完成：”，arg1，arg2）；clearTimeout（计时器）；cb（未定义，[arg1，arg2，“all good”]。join（“-”））；}},2000);});}const log=console.log.bind（控制台），info=console.info.bind（控制台，error=console.error.bind）；sampleFunc1（“sample1”，“promise”）.then（log）.catch（error）；local.sampleFunc2（“sample2”，“promise”）.then（log）.catch（error）；sampleFunc3（“sample3”，“promise”）.then（log）.catch（error）；sampleFunc4（“sample4”，“promise”）.then（log）.catch（error）；sampleFunc1（“sample1”，“回调”，信息）；local.sampleFunc2（“sample2”，“回调”，信息）；sampleFunc3（“sample3”，“回调”，信息）；sampleFunc4（“sample4”，“回调”，信息）；sampleFunc1（“sample1”，“promise pass”）.then（log）.catch（error）；local.sampleFunc2（“sample2”，“pr”

2021-06-15 03:42:43

使用普通的javaScript，这里有一个承诺api回调的解决方案。

function get(url, callback) {
        var xhr = new XMLHttpRequest();
        xhr.open('get', url);
        xhr.addEventListener('readystatechange', function () {
            if (xhr.readyState === 4) {
                if (xhr.status === 200) {
                    console.log('successful ... should call callback ... ');
                    callback(null, JSON.parse(xhr.responseText));
                } else {
                    console.log('error ... callback with error data ... ');
                    callback(xhr, null);
                }
            }
        });
        xhr.send();
    }

/**
     * @function promisify: convert api based callbacks to promises
     * @description takes in a factory function and promisifies it
     * @params {function} input function to promisify
     * @params {array} an array of inputs to the function to be promisified
     * @return {function} promisified function
     * */
    function promisify(fn) {
        return function () {
            var args = Array.prototype.slice.call(arguments);
            return new Promise(function(resolve, reject) {
                fn.apply(null, args.concat(function (err, result) {
                    if (err) reject(err);
                    else resolve(result);
                }));
            });
        }
    }

var get_promisified = promisify(get);
var promise = get_promisified('some_url');
promise.then(function (data) {
        // corresponds to the resolve function
        console.log('successful operation: ', data);
}, function (error) {
        console.log(error);
});
2016-11-28 03:07:12

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