I have a button user can click on that makes an http call to fetch data.
When user click the button the first time, I make http call. If the user clicks the button again, just provide the data that was fetched earlier.
How do I do that without storing it in a local variable explicitly? I have tried few things but none seem to work. It always makes the http request. I have tried to use "shareReplay" and "share" operators.
<button (click)=getData()>Click me</button>
getData() {
source$.pipe(
switchMap(sourceVal => {
const source2$ = this.getSource2();
const source3$ = this.getSource3(); -------- I do not want this call to be made on subsequent button clicks because it's a reference data
return combineLatest([source2$, source3$])
}),
map(([source2Val, source3Val]) => {
//do some processing
return 'done'
})
)
}
I am using angular and rxjs.
you can disable the button or prevent sending multiple requests via a variable.
fetching = false;
getData() {
if(!this.fetching) {
this.fetching = true;
this.http.get('url').pipe(shareReplay(1), finalize(() => {
this.fetching = false;
}));
}
}
Related
The below is my .ts file for the Alarm Component and over HTML I am using a simple *ngFor over criticalObject.siteList to display the records
This is not the original code I have simplified this but the problem I am facing is that on rigorous click on the refresh button(fires HTTP request), the list is adding duplicate siteNames and that should not happen. I have heard of debounce time, shareReplay, and trying applying here, which even doesn't make sense here.
NOTE: I have to fire the HTTP request on every refresh button click.
Keenly Waiting for Help.
criticalObject.siteList = [];
siteList = ["c404", "c432"];
onRefresh() {
this.criticalObject.siteList = [];
this.siteList.forEach(elem => {
getAlarmStatus(elem);
})
}
getAlarmStatus(item) {
critical_list = [];
alarmService.getAlarmStatusBySite(item.siteName).subcribe(data => {
if(data) {
// do some calculations
if(this.criticalObject.siteList.length === 0) {
this.criticalObject.siteList.push({
siteName = item.siteName;
})
}
this.criticalObject.siteList.forEach((elem, idx) => {
if(elem.siteName === item.siteName) {
return;
} else if(idx === this.criticalObject.siteList.length - 1) {
this.criticalObject.siteList.push({
siteName = item.siteName;
})
}
})
}
}
})
I did a silly mistake, I am new to JavaScript, I found out you cannot return from a forEach loop and that's why I was getting duplicated records, return statement in forEach acts like a continue in JavaScript.
I'm trying to build a simple app that lets the user type a name of a movie in a search bar, and get a list of all the movies related to that name (from an external public API).
I have a problem with the actual state updating.
If a user will type "Star", the list will show just movies with "Sta". So if the user would like to see the actual list of "Star" movies, he'd need to type "Star " (with an extra char to update the previous state).
In other words, the search query is one char behind the State.
How should it be written in React Native?
state = {
query: "",
data: []
};
searchUpdate = e => {
let query = this.state.query;
this.setState({ query: e }, () => {
if (query.length > 2) {
this.searchQuery(query.toLowerCase());
}
});
};
searchQuery = async query => {
try {
const get = await fetch(`${API.URL}/?s=${query}&${API.KEY}`);
const get2 = await get.json();
const data = get2.Search; // .Search is to get the actual array from the json
this.setState({ data });
} catch (err) {
console.log(err);
}
};
You don't have to rely on state for the query, just get the value from the event in the change handler
searchUpdate = e => {
if(e.target.value.length > 2) {
this.searchQuery(e.target.value)
}
};
You could keep state updated as well if you need to in order to maintain the value of the input correctly, but you don't need it for the search.
However, to answer what you're problem is, you are getting the value of state.query from the previous state. The first line of your searchUpdate function is getting the value of your query from the current state, which doesn't yet contain the updated value that triggered the searchUpdate function.
I don't prefer to send api call every change of letters. You should send API just when user stop typing and this can achieved by debounce function from lodash
debounce-lodash
this is the best practise and best for user and server instead of sending 10 requests in long phases
the next thing You get the value from previous state you should do API call after changing state as
const changeStateQuery = query => {
this.setState({query}, () => {
//call api call after already changing state
})
}
I want fetch data from firebase after that I want to execute another function. Second function have to wait until first one is complete .
this.oAngularFireDatabase.database.ref('Users').orderByKey()
.on('value', snapshot => {
if (snapshot.hasChildren()) {
snapshot.forEach(innerSnap => {
if (innerSnap.hasChild(user.uid)) {
//User role key
this.loggedInUserUserRoleKey = innerSnap.key;
//User id
this.loggedInUserId = user.uid;
//User name
this.loggedInUserName = innerSnap.child(user.uid).child("user_name").val();
if (innerSnap.child(user.uid).hasChild("user_image")) {
//User Image
this.loggedInUserImage = innerSnap.child(user.uid).child("user_image").val();
}
return false;
}
})
}
})
I can't call then function after on it gives me an error.
In my above code, I want call another function after all data are fetch from firebase.
The Firebase on() method can fire multiple times: once when it initially loads the data, and again whenever the data changes. Since a promise (the thing you call then() on) can only resolve once, on() can't return a promise.
There are two options here:
You want to only load the data once.
If this is the case, you should use Firebase's once() method, which does return a promise.
this.oAngularFireDatabase.database.ref('Users').orderByKey()
.once('value').then(snapshot => {
if (snapshot.hasChildren()) {
snapshot.forEach(innerSnap => {
if (innerSnap.hasChild(user.uid)) {
//User role key
this.loggedInUserUserRoleKey = innerSnap.key;
//User id
this.loggedInUserId = user.uid;
//User name
this.loggedInUserName = innerSnap.child(user.uid).child("user_name").val();
if (innerSnap.child(user.uid).hasChild("user_image")) {
//User Image
this.loggedInUserImage = innerSnap.child(user.uid).child("user_image").val();
}
return false;
}
})
}
}).then(value => {
// TODO: perform subsequent action on boolean value
})
You want to listen for changes on the data too.
If this is the case, you should put the subsequent action you want to take into the on() callback:
this.oAngularFireDatabase.database.ref('Users').orderByKey()
.on('value', snapshot => {
if (snapshot.hasChildren()) {
snapshot.forEach(innerSnap => {
if (innerSnap.hasChild(user.uid)) {
//User role key
this.loggedInUserUserRoleKey = innerSnap.key;
//User id
this.loggedInUserId = user.uid;
//User name
this.loggedInUserName = innerSnap.child(user.uid).child("user_name").val();
if (innerSnap.child(user.uid).hasChild("user_image")) {
//User Image
this.loggedInUserImage = innerSnap.child(user.uid).child("user_image").val();
}
}
})
// TODO: perform subsequent action on data
}
})
Note that both of these operations look pretty expensive for what they're trying to accomplish: scanning a JSON tree for a specific value is an anti-pattern in Firebase, and typically means you should modify/augment your JSON to allow a direct lookup or query.
For example, I suspect you now have a structure like /Users/$randomkey/$uid: { ..user data... }. For better performance, consider storing the user data directly under their UID: /Users/$uid: { ..user data... }. This removes the need for a query, and allows you to directly load the data for a user from this.oAngularFireDatabase.database.ref('Users').child(user.uid).
Let us say I am making multiple API calls from a React application. "Multiple API Calls" in this context means: Clicking on a checkbox several time fast. Everytime a checkbox is checked, an API call is triggered.
To illustrate this situation more precisely, I will add a screenshot off the User Interface:
Everytime a checkbox is checked, this function is called:
export function getApplications(authenticationToken, url, query, queryStringIn) {
return function(dispatch) {
const config = {
headers: {'Authorization' :"Bearer " + authenticationToken}
};
let queryString;
if (queryStringIn === "" || queryStringIn === null) {
queryString = queryStringBuilder.buildQuery(query);
} else {
queryString = queryStringIn;
}
let fetchTask = fetch(url + "/Applications?" + queryString.toString(), config).then(data => {
return data.json();
}).then(applications => {
dispatch(loadApplicationsSuccess(applications, queryString, query));
}).catch(error => {
dispatch(loadApplicationsFailed(error));
});
addTask(fetchTask); //ensure that server rendering is waiting for this to complete
return fetchTask;
}
The problem occurs when I am clicking at a checkbox so fast that the API is not able to return a response, before I am making a new call to the same API.
I want a behavior where only the last API call is made, and API calls in the queue before are cancelled if there are any.
What do you guys recommend to do in a such case?
I'm using angular-http-auth for intercepting 401 response in order to display login dialogue and when the user is authorized, to retry failed request.
Since I'm using infinity-scroll I'm increasing an offset value, with every additional upload:
var upload = function () {
dataResource.query($scope.model).then(function (result) {
angular.forEach(result.items, function (value) {
$scope.items.push(value);
});
});
}
$scope.uploadMore = function () {
$scope.model.Offset = $scope.model.Offset + 10;
upload();
};
upload();
When my page loads up it immediately sends 2 request to server upload(), invoked from this directive, and uploadMore() by infinity-scroll.
However, after user has logged in, the page does not display the first 10 entries, instead it displays 11-20 items 2 times in a row.
When I tried to debug it, I noticed that when angular-http-auth retries requests it uses increased by 10 Offset value for both queries($scope.module argument).
Functions upload() and uploadMore() are running for 2 times before angular-http-auth, so I guess that is why interceptor uses updated argument for both queries.
Could somebody please help me with this problem?
So you can resolve this problem prevent execute request until previous will finish.
The faster way to do that is :
var pending = false;
var upload = function () {
if(!pending) {
pending = true;
dataResource.query($scope.model).then(function (result) {
pending = false;
angular.forEach(result.items, function (value) {
$scope.items.push(value);
});
});
}
}