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？
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)
}
}
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
在Node.JS中将函数转换为promise之前
var request = require('request'); //http wrapped module
function requestWrapper(url, callback) {
request.get(url, function (err, response) {
if (err) {
callback(err);
}else{
callback(null, response);
}
})
}
requestWrapper(url, function (err, response) {
console.log(err, response)
})
转换后
var request = require('request');
function requestWrapper(url) {
return new Promise(function (resolve, reject) { //returning promise
request.get(url, function (err, response) {
if (err) {
reject(err); //promise reject
}else{
resolve(response); //promise resolve
}
})
})
}
requestWrapper('http://localhost:8080/promise_request/1').then(function(response){
console.log(response) //resolve callback(success)
}).catch(function(error){
console.log(error) //reject callback(failure)
})
如果您需要处理多个请求
var allRequests = [];
allRequests.push(requestWrapper('http://localhost:8080/promise_request/1'))
allRequests.push(requestWrapper('http://localhost:8080/promise_request/2'))
allRequests.push(requestWrapper('http://localhost:8080/promise_request/5'))
Promise.all(allRequests).then(function (results) {
console.log(results);//result will be array which contains each promise response
}).catch(function (err) {
console.log(err)
});
在Node.js 8中，您可以使用此npm模块动态地promisify对象方法：
https://www.npmjs.com/package/doasync
它使用util.provify和代理，使对象保持不变。Memoization也使用WeakMaps完成）。以下是一些示例：
使用对象：
const fs = require('fs');
const doAsync = require('doasync');
doAsync(fs).readFile('package.json', 'utf8')
.then(result => {
console.dir(JSON.parse(result), {colors: true});
});
具有以下功能：
doAsync(request)('http://www.google.com')
.then(({body}) => {
console.log(body);
// ...
});
您甚至可以使用本机调用和应用来绑定某些上下文：
doAsync(myFunc).apply(context, params)
.then(result => { /*...*/ });
