[英]How to return a nodejs callback as a number, from a JSON object property value?
[英]Nodejs express assign value from callback to object
我正在尝试编写一个简短的应用程序来测试IOTA nano交易。 说到异步编程,我是菜鸟。 请原谅我没有看到明显的事情。
我的问题:如何在适当的时候将回调函数的值分配给对象。
下面的代码解释:这些是我的nodejs express应用程序的片段。 我使用控制器,路由器和钱包模型。
当使用iota库请求服务(iri)时,我只有异步功能可以使用。 在以下情况下,我想收到我的钱包的IOTA地址。 这与服务很好地配合,我可以通过将生成的地址写入console.log进行测试。
但是,可能是因为回调函数是在所有其他函数之后执行的,所以我找不到将其写入我的钱包对象并接收它以在showPaymentInstructionsAction中显示它的方法。
到目前为止,我的解释是:
你有什么可以帮我的吗?
我是否会错过异步编程中的基本模式?
我不应该尝试从回调中接收值吗?
我应该了解Promise来解决这个问题吗?
最好的问候,Peterobjec
'use strict'
class Wallet{
constructor(iota_node, seed){
this.seed = seed;
this.receivingAddress = "empty";
this.iota_node = iota_node;
}
generateAddress() {
this.iota_node.api.getNewAddress(this.seed, {'checksum': true}, postResponse)
function postResponse(error,address) {
if (!error) {
// callback won't assigned to my wallet object.
// I can probably use (function).bind(this);
// But this doesn't solve the timing issue
this.receivingAddress = address
// console.log shows, the address is generated correctly
// but how can I get it into my object? and retreive it after it is written?
console.log("address callback: %s", this.receivingAddress)
}else{
console.log(e.message);
}
}
}
getReceivingAddress(){
// I never managed to get this filled by the callback
console.log("in getReceivingAddress: %s", this.receivingAddress)
return this.receivingAddress;
}
}
// The controller
var config = require('../config.js'),
Wallet = require('./model_wallet'),
IOTA = require('iota.lib.js');
function orderRequestAction(req, res, next){
// IOTA Reference Implementation
var iri = new IOTA({
'host': 'http://localhost',
'port': 14265
});
res.locals.wallet = new Wallet(iri, config.wallet.seed);
res.locals.wallet.generateAddress()
}
function showPaymentInstructionsAction(req, res){
res.render('paymentInstructions', {
title:"payment instructions",
receivingAddress: res.locals.wallet.getReceivingAddress()
})
}
// Router
var controller = require('./controller');
module.exports = function(app){
app.post('/orderRequest', controller.orderRequestAction, controller.showPaymentInstructionsAction);
};
您可以删除getReceivingAddress函数并像这样使用generateAddress(),
generateAddress() {
return new Promise((resolve, reject) => {
this.iota_node.api.getNewAddress(this.seed, {'checksum': true}, (error,address) => {
if (!error) {
// callback won't assigned to my wallet object.
// I can probably use (function).bind(this);
// But this doesn't solve the timing issue
this.receivingAddress = address
// console.log shows, the address is generated correctly
// but how can I get it into my object? and retreive it after it is written?
console.log("address callback: %s", this.receivingAddress)
resolve(address); // You will get this while calling this function as shown next
}else{
console.log(e.message);
reject(error);
}
})
})
}
现在,在调用该函数时,您需要在需要调用的地方使用该函数,
...
generateRecievingAddress().then(function(address){
// here address is what you resolved earlier
}).catch(function(error){
// error is what you rejected
})
我希望这可以澄清您的疑问。
当您熟悉Promises时,您可能想使用es7语法来编写异步代码,即使用async和await。 您还可以在这里阅读更多信息
演示片段
class XYZ {
constructor() {
this.x = 15;
}
getX() {
return new Promise((resolve, reject) => {
if(true){
resolve(this.x); // inside Promise
}
else{
reject(new Error("This is error"));
}
})
}
}
const xObj = new XYZ();
xObj.getX().then(function(x){
console.log(x);
}).catch(function(){
console.log(error);
})
这将记录15。
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