promise resolution seen in multiple controllers - javascript

I want two different controllers to run different functions after some promises are resolved in a service (i dont want this service to make an http request each time a controller needs the data, I only want one http request).
I have a service that makes a request and gets a promise. I want controller1 to see this resolution and then run some code. I then want controller2 to also see that this promise resolves and run some code (basically multiple then() methods that run on the same promise but from different files). How can I go about doing this?
All the examples I have seen have one controller running code after a certain promise resolves, but not multiple controllers listening for the same promise to resolve.
here is some code im borrowing from this article (ill add a 'mother controller' to illustrate my example, I dont want the son service to ever make his http call twice): http://andyshora.com/promises-angularjs-explained-as-cartoon.html
son service
app.factory('SonService', function ($http, $q) {
return {
getWeather: function() {
// the $http API is based on the deferred/promise APIs exposed by the $q service
// so it returns a promise for us by default
return $http.get('http://fishing-weather-api.com/sunday/afternoon')
.then(function(response) {
if (typeof response.data === 'object') {
return response.data;
} else {
// invalid response
return $q.reject(response.data);
}
}, function(response) {
// something went wrong
return $q.reject(response.data);
});
}
};
});
father Controller:
// function somewhere in father-controller.js
var makePromiseWithSon = function() {
// This service's function returns a promise, but we'll deal with that shortly
SonService.getWeather()
// then() called when son gets back
.then(function(data) {
// promise fulfilled
if (data.forecast==='good') {
prepareFishingTrip();
} else {
prepareSundayRoastDinner();
}
}, function(error) {
// promise rejected, could log the error with: console.log('error', error);
prepareSundayRoastDinner();
});
};
Mother Controller:
var makePromiseWithSon = function() {
SonService.getWeather()
// then() called when son gets back
.then(function(data) {
// promise fulfilled
if (data.forecast==='good') {
workInTheGarden();
} else {
sweepTheHouse();
}
}, function(error) {
// promise rejected, could log the error with: console.log('error', error);
sweepTheHouse();
});
};

To have your factory service only get the url once, store the httpPromise in your factory service.
app.factory('SonService', function ($http) {
var weatherPromise;
function getWeather() {
return $http.get('http://fishing-weather-api.com/sunday/afternoon')
.then(function(response) {
if (typeof response.data === 'object') {
return response.data;
} else {
// invalid response
throw response;
}
}, function(response) {
// something went wrong
throw response;
});
}
function sonService() {
if (!weatherPromise) {
//save the httpPromise
weatherPromise = getWeather();
}
return weatherPromise;
}
return sonService;
});

The simple answer, in a non-angular-specific (but really easy to apply to Angular) way, is to create a service which caches ON-OUTBOUND-REQUEST (rather than caching return values, like most systems would).
function SearchService (fetch) {
var cache = { };
return {
getSpecificThing: function (uri) {
var cachedSearch = cache[uri];
if (!cachedSearch) {
cachedSearch = fetch(uri).then(prepareData);
cache[uri] = cachedSearch;
}
return cachedSearch;
}
};
}
function A (searchService) {
var a = this;
Object.assign(a, {
load: function ( ) {
searchService.getSpecificThing("/abc").then(a.init.bind(a));
},
init: function (data) { /* ... */ }
});
}
function B (searchService) {
var b = this;
Object.assign(b, {
load: function ( ) {
searchService.getSpecificThing("/abc").then(b.init.bind(b));
},
init: function (data) { /* ... */ }
});
}
var searchService = SearchService(fetch);
var a = new A(searchService);
var b = new B(searchService);
a.load().then(/* is initialized */);
b.load().then(/* is initialized */);
They're sharing the same promise, because the service they were talking to cached and returned the same promise.
If you wanted to be safe, you could cache a promise and then return new instances of promises which resolve (or reject) based on the cached promise.
// instead of
return cachedSearch;
// replace it with
return Promise.resolve(cachedSearch);
Each user is now getting a new instance, every time you make a request, but each instance is also passing or failing based on the original cached call.
And of course you can take it further, and put a time-limit on the cache, or have hooks to invalidate the cache, or whatever...
Converting this to Angular is also a snap
SearchService is a service
A and B are controllers
use $http instead of fetch (though fetch is really pretty)
in fetch( ).then(prepareData) you'd be converting data from JSON on success;
in $http, you'd be returning response.data because your users don't want to have to do that
either way, you're performing that operation exactly once, per outbound call, so cache it, too
use $q (and q methods) instead of native Promise
use angular.extend, instead of Object.assign
You're done; you've now ported that whole concept into Angular AND VanillaJS

Related

How to get response from AngularJS $http.get().then()

I've recently started to upgrade from Bootstrap 3 to Bootstrap 4, and that requires I also upgrade from AngularJS 1.5.8 to a minimum of AngularJS 1.6.1. I have a simple AngularJS/MVC application with the following code setup:
/scripts/app.js (contains routing)
/scripts/controllers.js (contains controllers, method calls, etc)
/scripts/services.js (contains the callback methods that hit the C# controllers and bring back data, or "do things" (CRUD methods)
In my controllers.js, I have a method:
function init() {
api.initialIndexLoad(
function(result) {
if (result.error) {
notificationService.danger("<h5>An error occurred.</h5><h6>Details: {0}</h6>".format(result.error));
} else {
vm.dataList = result.theDataFromCSharp;
}
vm.loaded = true;
}
);
}
init();
This makes a call to my services.js, where I have this code:
"use strict";
angular
.module("CustList.services", ["ngResource"])
.service("api",
function api($resource, $http, notificationService) {
function handleError(err, fn) {
if (!fn) {
notificationService.error(err);
} else {
fn(err);
}
}
return {
initialIndexLoad: function(callback, error) {
$http.get("/Customers/InitialIndexLoad")
.success(callback)
.error(function(e) {
handleError(e, error);
});
}
};
}
);
So, of course, after updating my libraries to AngularJS 1.6.1 (Actually, I went straight to AngularJS 1.7.5), I started to get errors, and after a while figured out that the promise syntax had changed. So I tried to change with it, and updated my services.js to be:
"use strict";
angular
.module("CustList.services", ["ngResource"])
.service("api",
function api($resource, $http, notificationService) {
function handleSuccess(response) {
return response.data;
}
function handleError(err, fn) {
if (!fn) {
notificationService.error(err);
} else {
fn(err);
}
}
return {
initialIndexLoad: function() {
$http
.get("/Customers/InitialIndexLoad")
.then(handleSuccess)
.catch(handleError);
}
};
}
);
The errors went away, and I thought I had this upgrade licked, until I realized: I wasn't actually getting the data back! That new handleSuccess method I'd created was getting the data in the response, but the return response.data wasn't returning the data back to my controllers.js method, so I could plug it into vm.dataList.
It doesn't throw an error - it just does nothing. I'd appreciate help figuring this out!
The service method needs to return the $http promise.
app.service("api",
function api($http, notificationService) {
function handleSuccess(response) {
return response.data;
}
function handleError(err) {
notificationService.error(err);
throw err;
}
return {
initialIndexLoad: function() {
̶$̶h̶t̶t̶p̶
return $http
.get("/Customers/InitialIndexLoad")
.then(handleSuccess)
.catch(handleError);
}
};
}
);
Notice that the errorHandler needs to re-throw the error. Otherwise the handler will convert the rejected promise to a fulfilled promise.
The controller needs to use the .then and .catch methods:
function init() {
var promise = api.initialIndexLoad();
promise.then(function(result) {
if (result.error) {
notificationService.danger("<h5>An error occurred.</h5><h6>Details: {0}</h6>".format(result.error));
} else {
vm.dataList = result.theDataFromCSharp;
}
vm.loaded = true;
}).catch(functions(err) {
console.log(err);
throw err;
});
}
The .then method returns a new promise which is resolved or rejected via the return value of the successCallback, errorCallback (unless that value is a promise, in which case it is resolved with the value which is resolved in that promise using promise chaining.
For more information, see
AngularJS $q Service API Reference - The Promise API
You're Missing the Point of Promises
Return inside of initialIndexLoad
so
return $http
.get("/Customers/InitialIndexLoad")
.then(handleSuccess)
.catch(handleError);
Would guess this is it, maybe lost during refactor/upgrade.

How to reload a http.get request after performing a function

I am trying to delete a post from a list. The delete function is performing by passing serially to a delete function showed below.
$scope.go = function(ref) {
$http.get("api/phone_recev.php?id="+ref)
.success(function (data) { });
}
After performing the function, I need to reload the http.get request which used for listing the list.
$http.get("api/phone_accept.php")
.then(function (response) { });
Once the function performed. The entire list will reload with new updated list. Is there any way to do this thing.
Try this
$scope.go = function(ref) {
$http.get("api/phone_recev.php?id="+ref)
.success(function (data) {
//on success of first function it will call
$http.get("api/phone_accept.php")
.then(function (response) {
});
});
}
function list_data() {
$http.get("api/phone_accept.php")
.then(function (response) {
console.log('listing');
});
}
$scope.go = function(ref) {
$http.get("api/phone_recev.php?id="+ref)
.success(function (data) {
// call function to do listing
list_data();
});
}
Like what #sudheesh Singanamalla says by calling the same http.get request again inside function resolved my problem.
$scope.go = function(ref) {
$http.get("api/phone_recev.php?id="+ref).success(function (data) {
//same function goes here will solve the problem.
});}
});
You can use $q - A service that helps you run functions asynchronously, and use their return values (or exceptions) when they are done processing.
https://docs.angularjs.org/api/ng/service/$q
Inside some service.
app.factory('SomeService', function ($http, $q) {
return {
getData : function() {
// the $http API is based on the deferred/promise APIs exposed by the $q service
// so it returns a promise for us by default
return $http.get("api/phone_recev.php?id="+ref)
.then(function(response) {
if (typeof response.data === 'object') {
return response.data;
} else {
// invalid response
return $q.reject(response.data);
}
}, function(response) {
// something went wrong
return $q.reject(response.data);
});
}
};
});
function somewhere in controller
var makePromiseWithData = function() {
// This service's function returns a promise, but we'll deal with that shortly
SomeService.getData()
// then() called when gets back
.then(function(data) {
// promise fulfilled
// something
}, function(error) {
// promise rejected, could log the error with: console.log('error', error);
//some code
});
};

How ensure async request has finished before running a function

I am performing an async request to pull data from a server and then call a function after the request. My question is how do I ensure the request is complete and all data loaded before processRecords() runs?
Thanks in advance.
function getRecords () {
var ids = Server.getIds();
var allTheRecords = [];
ids.forEach(function(recordId) {
Server.getRecord(recordId, function (error, data) {
if(error) {
console.log(error);
} else {
allTheRecords.push(data);
};
});
});
processRecords(allTheRecords);
}
How are you performing the Asynchronous request? If it's an AJAX request, the API provides for callbacks to be supplied based on the result of the call.
https://developer.mozilla.org/en-US/docs/Web/API/XMLHttpRequest
You could use the native Promise api to perform the async actions for you.
Using Promise.all you can give it an array of promises that need to be resolved before calling the processRecords function.
It also now more reusable as you have a getRecord function that you could use elsewhere in your code.
You should probably think of a way to add in the ability to get multiple records from the server if you control it though. You don't really want to fire off a bunch of network requests if you can do it in just one.
// Server mock of the api you have shown
const Server = {
getRecord(id, callback) {
console.log('getRecord', id)
callback(null, {id})
},
getIds() {
return [1, 2, 3]
}
}
function getRecords (ids, processRecords) {
console.log('getRecords', ids.join())
// mapping the array of id's will convert them to an
// array of Promises by calling getRecord with the id
Promise.all(ids.map(getRecord))
// then is called once all the promises are resolved
.then(processRecords)
// this will be called if the reject function of any
// promise is called
.catch(console.error.bind(console))
}
function getRecord(recordId) {
// this function returns a Promise that wraps your
// server call
return new Promise((resolve, reject) => {
Server.getRecord(recordId, function (error, data) {
if(error) {
reject(error)
} else {
resolve(data)
}
})
})
}
getRecords(Server.getIds(), function(records) {
console.log('resolved all promises')
console.log(records)
})

q service in node.js confusion

I don't understand below part
var q = require("q"),
BlogPost = require("../models/blogPost");
module.exports = {
getAllPosts: getAllPosts
};
function getAllPosts() {
var deferred = q.defer();
BlogPost
.find({})
.sort("-date")
.exec(function(error, posts) {
if (error) {
deferred.reject(error);
} else {
deferred.resolve(posts);
}
});
return deferred.promise;
}
I found above code in controller, but can't understand it. Why at the end we use return deferred.promise? How would I use the getAllPosts later? Can't we just return the posts objects?
You would consume a function that returns a promise like so:
var getAllPosts = require('./your-module-name.js').getAllPosts;
getAllPosts()
.then(function(posts) {
//successfully process the posts
})
.catch(function(err) {
//handle the error
})
.finally(function(){
//clean up anything you need to...
})
Promise is the just representation of the asynchronous result.
It has three states:
1-> success
-> Error
-> Pending
deferred is a just object of promise and it returns after processing one of above state.
We can use javascript code without promise but sometimes we have to give it to make our code execute as asynchronous way.
That's why we use promise

JS promise passing between functions / wait for promises

I am trying to work through JS Promises in node.js and don't get the solution for passing promises between different function.
The task
For a main logic, I need to get a json object of items from a REST API. The API handling itself is located in a api.js file.
The request to the API inthere is made through the request-promise module. I have a private makeRequest function and public helper functions, like API.getItems().
The main logic in index.js needs to wait for the API function until it can be executed.
Questions
The promise passing kind of works, but I am not sure if this is more than a coincidence. Is it correct to return a Promise which returns the responses in makeRequest?
Do I really need all the promises to make the main logic work only after waiting for the items to be setup? Is there a simpler way?
I still need to figure out, how to best handle errors from a) the makeRequest and b) the getItems functions. What's the best practice with Promises therefor? Passing Error objects?
Here is the Code that I came up with right now:
// index.js
var API = require('./lib/api');
var items;
function mainLogic() {
if (items instanceof Error) {
console.log("No items present. Stopping main logic.");
return;
}
// ... do something with items
}
API.getItems().then(function (response) {
if (response) {
console.log(response);
items = response;
mainLogic();
}
}, function (err) {
console.log(err);
});
api.js
// ./lib/api.js
var request = require('request-promise');
// constructor
var API = function () {
var api = this;
api.endpoint = "https://api.example.com/v1";
//...
};
API.prototype.getItems = function () {
var api = this;
var endpoint = '/items';
return new Promise(function (resolve, reject) {
var request = makeRequest(api, endpoint).then(function (response) {
if (200 === response.statusCode) {
resolve(response.body.items);
}
}, function (err) {
reject(false);
});
});
};
function makeRequest(api, endpoint) {
var url = api.endpoint + endpoint;
var options = {
method: 'GET',
uri: url,
body: {},
headers: {},
simple: false,
resolveWithFullResponse: true,
json: true
};
return request(options)
.then(function (response) {
console.log(response.body);
return response;
})
.catch(function (err) {
return Error(err);
});
}
module.exports = new API();
Some more background:
At first I started to make API request with the request module, that works with callbacks. Since these were called async, the items never made it to the main logic and I used to handle it with Promises.
You are missing two things here:
That you can chain promises directly and
the way promise error handling works.
You can change the return statement in makeRequest() to:
return request(options);
Since makeRequest() returns a promise, you can reuse it in getItems() and you don't have to create a new promise explicitly. The .then() function already does this for you:
return makeRequest(api, endpoint)
.then(function (response) {
if (200 === response.statusCode) {
return response.body.items;
}
else {
// throw an exception or call Promise.reject() with a proper error
}
});
If the promise returned by makeRequest() was rejected and you don't handle rejection -- like in the above code --, the promise returned by .then() will also be rejected. You can compare the behaviour to exceptions. If you don't catch one, it bubbles up the callstack.
Finally, in index.js you should use getItems() like this:
API.getItems().then(function (response) {
// Here you are sure that everything worked. No additional checks required.
// Whatever you want to do with the response, do it here.
// Don't assign response to another variable outside of this scope.
// If processing the response is complex, rather pass it to another
// function directly.
}, function (err) {
// handle the error
});
I recommend this blog post to better understand the concept of promises:
https://blog.domenic.me/youre-missing-the-point-of-promises/

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