Method chaining with Promises

Method chaining with Promises - javascript

I want to implement the classic method chain pattern, the final usage should be
DB
.push(2)
.push(3)
This is the current code, obviously doesn't work, I'm not clear how to return the reference to DB itself resolving the promise
let nodes = [];
let DB = {
self:this,
push: (i) => new Promise((resolve, reject) => {
nodes.push(i)
resolve(this)
})
}

Only a class or function instance has a this reference.
class DB {
constructor() {
this.nodes = [];
this.promise = Promise.resolve();
}
push(i) {
this.nodes.push(i);
return this;
}
pushAsync(i) {
return new Promise((resolve) => {
this.nodes.push(i);
resolve();
});
}
pushAsyncChain(i) {
this.promise.then(() => {
this.promise = new Promise((resolve) => {
this.nodes.push(i);
resolve();
});
});
return this;
}
then(callback) {
this.promise.then(callback);
}
}
const db = new DB();
db.push(2).push(3);
db.pushAsync(4).then(() => db.pushAsync(5));
db
.pushAsyncChain(6)
.pushAsyncChain(7)
.then(() => console.log(db.nodes)); // or await db.promise; console.log(db.nodes);

Related

How to call HttpException in setTimeout, when i wait promise a long time?

I get products from different servers, I want return exception, when wait a long time.
I have created setTimeout for this, but it stoped server and didn't return error.
How to fix it?
const server = 23;
const productsTimeout = setTimeout(() => { throw new HttpException('Problem', HttpStatus.INTERNAL_SERVER_ERROR) }, 3000);
products = await new Promise((resolve, reject) => {
this.socketClientCabinet.on('products_get', async ({ server, products }) => {
if (server === serverID) {
const {
productsSymbols,
} = this.productsTransform(products);
clearTimeout(productsTimeout);
resolve(productsSymbols);
}
});
});

User delete his answer, I have fixed it.
let productsTimeout;
const timeoutPromise = new Promise((res, rej) => {
instrumentsTimeout = setTimeout(() => rej(new HttpException('problem', 500)), 1000, )
})
const productsPromise = new Promise((resolve, reject) => {
this.socketClientCabinet.on('products_get', async ({ server, products }) => {
if (server === serverID) {
const {
productsSymbols,
} = this.productsTransform(products);
clearTimeout(productsTimeout);
resolve(productsSymbols);
}
});
});
const products = await Promise.race([
timeoutPromise,
productsPromise
])
It is work.

Async operations when instance created

I had a job interview yesterday, and I was given a coding challenge as the following:
// 3. Coding challenge.
// The goal is to make function1/function2 to work only when the constructor has finished its async operations.
// You CAN'T change the notifyUrls function. Imagine it's a 3th party library you don't have control on.
// CAN'T CHANGE THIS.
//===================
function notifyUrls(item, callback) {
asyncOperation(item).then((res) => {
callback(res);
});
}
//===================
const asyncOperation = () => { return new Promise((resolve, reject) => { setTimeout(() => { console.log('Timeout execute'); resolve(); }, 2000); }); };
const URL1 = 'http://www.somerestapi/get1';
const URL2 = 'http://www.somerestapi/get2';
const URL3 = 'http://www.somerestapi/get3';
class MyClass {
constructor() {
[URL1, URL2, URL3].forEach(item => {
notifyUrls(item, () => { });
});
}
myFunction1() {
// Only start working when constructor finished notifying.
// ...
console.log('myFunction1');
}
myFunction2() {
// Only start working when constructor finished notifying.
// ...
console.log('myFunction2');
}
}
And here is what I did:
// CAN'T CHANGE THIS.
//===================
function notifyUrls(item, callback) {
asyncOperation(item).then((res) => {
callback(res);
});
}
//===================
const asyncOperation = () => { return new Promise((resolve, reject) => { setTimeout(() => { console.log('Timeout execute'); resolve(); }, 2000); }); };
const URL1 = 'http://www.somerestapi/get1';
const URL2 = 'http://www.somerestapi/get2';
const URL3 = 'http://www.somerestapi/get3';
class MyClass {
constructor() {
this.ready = Promise.all([URL1, URL2, URL3].map((url) => { this.myAsyncCall(url); }));
}
myAsyncCall(item) {
return new Promise((resolve, reject) => {
notifyUrls(item, (res) => { resolve(res); });
});
}
async myFunction1() {
if (await this.ready) {
// Only start working when constructor finished notifying.
// ...
console.log('myFunction1');
}
}
myFunction2() {
// Only start working when constructor finished notifying.
// ...
console.log('myFunction2');
}
}
(async () => {
const myClass = new MyClass();
await myClass.myFunction1();
})();
But the output is:
myFunction1
Timeout execute
Timeout execute
Timeout execute
What I want the output to be is:
Timeout execute
Timeout execute
Timeout execute
myFunction1
How can I work around it?
Thanks.

The problem is in
this.ready = Promise.all([URL1, URL2, URL3].map((url) => { this.myAsyncCall(url); }));
Your map callback doesn't return anything
Either do
this.ready = Promise.all([URL1, URL2, URL3].map((url) => { return this.myAsyncCall(url); }));
or
this.ready = Promise.all([URL1, URL2, URL3].map((url) => this.myAsyncCall(url)));
Adding some coding tips
notifyUrls(item, (res) => {
resolve(res);
});
Can simply be
notifyUrls(item, resolve);
and
const asyncOperation = () => {
return new Promise((resolve, reject) => {
setTimeout(() => {
resolve();
}, 2000);
});
};
is just
const asyncOperation = () => new Promise(resolve => setTimeout(resolve, 2000));

Calling other functions of a class inside a Promise in Node

So, I have two methods in a class. Both returns a promise. The second function calls the first function from inside of the promise it returns.
module.exports = {
funcA: () => {
return new Promise((resolve, reject) => {
something ? resolve(something): reject('nope');
});
}
funcB: () => {
return new Promise(async(resolve, reject) => {
try {
const something = await this.funcA();
} catch(err) {
reject('error');
}
}
}
When I am trying to call funcB() from another class, like this:
let something = await someService.funcB();
I am getting:
TypeError: this.funcA() is not a function
Can you shed some light on why this is happening and how to solve this problem?

one way to make it work is to create the function outside of the module.exports block to get a reference of each function. Then this keyword can be omitted
const funcA = () => {
return new Promise((resolve, reject) => {
// code here
});
};
const funcB = () => {
return new Promise(async(resolve, reject) => {
try {
const something = await funcA();
resolve(something);
} catch(err) {
reject('error');
}
})
};
module.exports = {
funcA,
funcB
}

I think this is what you need to do
module.exports = {
funcA: function() {
return new Promise((resolve, reject) => {
something ? resolve(something): reject('nope');
});
}
funcB: function() {
return new Promise(async(resolve, reject) => {
try {
const something = await this.funcA();
} catch(err) {
reject('error');
}
}
}
I've found using arrow functions inside objects as you've done breaks this, but you can fix it this way.

check if user in group ActiveDirectory.js node.js

In c# I would write something like this:
bool HasRole(string userName, string[] groupNames)
{
var ad = new ActiveDirectory();
return groupsNames.Any(groupName => ad.IsUserInGroup(userName, groupName);
}
and then just
if (HasRole("UserName", new[] {"group1", "group2"}))
//do something
in javascript it looks like all things are doing asynchronously, I've read about promises and so on, and tried this:
const ActiveDirectory = require('activedirectory2');
const Promise = require('promise');
const globals = require('./globals');
const activeDirectory = new ActiveDirectory(globals.AdConfig);
hasRole(msg, ...groupNames) {
if (groupNames == null || groupNames == undefined || groupNames.length == 0)
return false;
let promises = [];
groupNames.forEach(groupName => {
let promise = new Promise((resolve, reject) => {
activeDirectory.isUserMemberOf(msg.envelope.user.name, groupName, function (err, isMember) {
if (err) {
reject(err)
}
resolve(isMember);
});
});
promises.push(promise);
});
//I don't clearly understand how I can return promise result only or promise with the right result
let hasRole = false;
promises.forEach(promise => promise.done(result => {
if (result)
hasRole = result;
}));
return hasRole;
So how can write something like:
if (hasRole(msg, 'group1', 'group2'))
//do something...
I suppose I should return promise but how I can do it if i need to check multiple groups?
UPDATE
I wrapped the forEach loop in promise:
return new Promise((resolve, reject) => {
promises.forEach(promise => promise.done(result => {
if (result)
return resolve(result);
}));
and then:
hasRole(msg, 'group1', 'group2').done(result => {
if (result)
//do...
});
May there is another way?

Found a solution. Promises.all is what i needed.
Result code:
hasRole(msg, ...groupNames) {
let promises = [];
groupNames = groupNames.filter(x => x.trim().length > 0);
if (groupNames == undefined || groupNames.length == 0)
{
promises.push(new Promise.resolve(false));
return Promise.all(promises);
}
groupNames.forEach(groupName => {
let promise = new Promise((resolve, reject) => {
activeDirectory.isUserMemberOf(msg.envelope.user.name, groupName, function (err, isMember) {
if (err) {
reject(err)
}
resolve(isMember);
});
});
promises.push(promise);
});
return Promise.all(promises);
}

Synchronized in typescript angular 5

I have the following code.
public async getOrderInforAsync(customerOrderId) {
return new Promise((resolve, reject) => {
this.orderEntryService.getCommissionIncentives(customerOrderId)
.subscribe(
response => {
Object.assign(this.order, response);
this.order.bookingDate = this.order.bookingDate ? new Date(this.order.bookingDate) : null;
this.order.estBillDate = this.order.estBillDate ? new Date(this.order.estBillDate) : null;
this.order.orderSplit.forEach(element => {
element.rcNumberFullName = `${this.order.customerOrderRCNumber}${element.rcNumberSuffix}`;
});
this.initialQuantityAllocated();
this.orderSummary.allocatedEstCommissionPercent = this.calculateTotalOrderPercent();
this.orderSummary.allocatedEstCommissionAmount = this.calculateTotalOrderAmount();
this.highlight = this.checkOrderSummary(this.orderSummary.allocatedEstCommissionPercent, this.orderSummary.allocatedEstCommissionAmount);
this.calculateAllocatedActualPercent();
this.calculateAllocatedActualAmount();
this.onChangeEstSalesPrice();
resolve();
},
error => {
reject();
}
);
});
}
Sometimes the resolve() is called before this.calculateAllocatedActualPercent() and this.calculateAllocatedActualAmount() are done.
So how to make this code run synchronized, it means all functions on this block code had done before resolve() called?

Try this :
public async getOrderInforAsync(customerOrderId) {
return new Promise((resolve, reject) => {
this.orderEntryService.getCommissionIncentives(customerOrderId)
.subscribe(
response => {
Object.assign(this.order, response);
this.order.bookingDate = this.order.bookingDate ? new Date(this.order.bookingDate) : null;
this.order.estBillDate = this.order.estBillDate ? new Date(this.order.estBillDate) : null;
this.order.orderSplit.forEach(element => {
element.rcNumberFullName = `${this.order.customerOrderRCNumber}${element.rcNumberSuffix}`;
});
this.initialQuantityAllocated();
this.orderSummary.allocatedEstCommissionPercent = this.calculateTotalOrderPercent();
this.orderSummary.allocatedEstCommissionAmount = this.calculateTotalOrderAmount();
this.highlight = this.checkOrderSummary(this.orderSummary.allocatedEstCommissionPercent, this.orderSummary.allocatedEstCommissionAmount);
await this.calculateAllocatedActualPercent();
await this.calculateAllocatedActualAmount();
this.onChangeEstSalesPrice();
resolve();
},
error => {
reject();
}
);
});
}
async calculateAllocatedActualPercent(){
return new Promise(resolve,reject){
// call api
if (data)
resolve(data);
else
reject()
}
}
async calculateAllocatedActualAmount(){
return new Promise(resolve,reject){
// call api
if (data)
resolve(data);
else
reject()
}
}

An async function returns a Promise. And to declare a function as async, you need to have an await call inside it.
Change your observable returned from this.orderEntryService.getCommissionIncentives(customerOrderId) .toPromise() and then await it.
Try this:
public async getOrderInforAsync(customerOrderId) {
try {
const response = await this.orderEntryService
.getCommissionIncentives(customerOrderId).toPromise();
this.order = { ...response };
this.order.bookingDate = this.order.bookingDate ? new Date(this.order.bookingDate) : null;
this.order.estBillDate = this.order.estBillDate ? new Date(this.order.estBillDate) : null;
for (let i = 0; i < this.order.orderSplit; i++) {
const element = this.order.orderSplit[i];
element.rcNumberFullName = `${this.order.customerOrderRCNumber}${element.rcNumberSuffix}`
}
this.initialQuantityAllocated();
this.orderSummary.allocatedEstCommissionPercent = this.calculateTotalOrderPercent();
this.orderSummary.allocatedEstCommissionAmount = this.calculateTotalOrderAmount();
this.highlight = this.checkOrderSummary(this.orderSummary.allocatedEstCommissionPercent, this.orderSummary.allocatedEstCommissionAmount);
this.calculateAllocatedActualPercent();
this.calculateAllocatedActualAmount();
this.onChangeEstSalesPrice();
return response;
} catch (error) {
return error;
}
}

Develop Reference

JavaScript is the programming language of the Web.

Method chaining with Promises - javascript

Related

How to call HttpException in setTimeout, when i wait promise a long time?

Async operations when instance created

Calling other functions of a class inside a Promise in Node

check if user in group ActiveDirectory.js node.js

Synchronized in typescript angular 5

Categories

Resources