I am running redux on node. To handle asynchronous actions, like reading a file or listing of a directory, I am using redux-thunk in combination with Promises. So a typical action can look like that:
const
fs = require('fs'),
{ promisify } = require('util'),
readdir = promisify(fs.readdir);
const listFiles = dir => dispatch =>
readdir(dir)
.then(files => dispatch({
type: '…',
payload: { files }
}));
So:
try {
store.dispatch(listFiles('/some/path'));
catch (error) {
//some rescue plan here,
//won't work if directory not exists
}
wont work here, because the action is asynchronous and right now, the only way I see to handle all errors is to add a .catch() to all promises in all actions and dispatch an error action there.
That has two downsides:
a lot of code repetition and
i need to know all possible errors in ahead.
So my question is: Is there any way to create a global error handler, which will also be called if an asynchronous action fails, such that I can add some error indicating information to the state, which can be displayed?
Could that be possible with a »storeEnhancer« or some »middleware«?
UPDATE
I could find something that is really helpful:
process.on('unhandledRejection', (reason, promise) => {
console.log(reason.message);
});
That callback is triggered whenever a Promise is rejected and no catch block is added. Right now that seams to do the trick, but anyway, I would prefer a solution that basically does the exact same thing, but only for rejected Promises which are triggered within store.dispatch(), so only when an error within the processing of actions/middleware/reducers within redux comes to happen.
If you're looking for a redux middleware solution, take a look at redux-catch.
Related
Expo React Native SDK Version: 46
Platforms: Android/iOS
Package concerned : Expo.Updates
Hello everyone, I want to programmatically check for new updates, without using the fallbackToCacheTimeout in app.json that will trigger the check of the new updates when the application is launched because like that I can't put a custom loading page.
So by doing this all by code as follow :
try{
const update = await Updates.checkForUpdateAsync();
if(update.isAvailable){
await Updates.fetchUpdateAsync();
await Updates.reloadAsync();
}else{}
}catch(err){}
But I want to be able to abort all those calls after a certain time (thus, the user that have a bad connection can use the app without waiting a very long time).
I check the documentation and I cannot found any method that allow this.
I dont't think it's possible to cancel a Promise for now in Javascript, or maybe any connection ?
Or does the "fallbackToCacheTimeout" value in the app.json will automatically apply to the fetch updates call of the Expo API?
Do someone have any idea how to do it ? :(
First of all I am assuming you have set updates.checkautomatically field to ON_ERROR_RECOVERY in app.json or app.config.js file. If not, please check the documentation. The reason why you need this is to avoid automatic updates which can also block your app on splash screen.
Updated Solution
Because of the limitation in javascript we can't cancel any external Promise (not created by us or when its reject method is not exposed to us). Also the function fetchUpdateAsync exposed to us is not a promise but rather contains fetch promise and returns its result.
So, here we have two options:
Cancel reloading the app to update after a timeout.
But note that updates will be fetched in background and stored on
the device. Next time whenever user restarts the app, update will
be installed. I think this is just fine as this approach doesn't
block anything for user and also there is a default timeout for http
request clients like fetch and axios so, request will error out in
case of poor/no internet connection.
Here is the code:
try {
const update = await Updates.checkForUpdateAsync();
if (update.isAvailable) {
const updateFetchPromise = Updates.fetchUpdateAsync();
const timeoutInMillis = 10000; // 10 seconds
const timeoutPromise = new Promise((_, reject) => setTimeout(() => reject("timedout"), timeoutInMillis))
// This will return only one Promise
Promise.race([updateFetchPromise, timeoutPromise])
.then(() => Updates.reloadAsync())
.catch((error) => {
if (error === 'timedout') {
// Here you can show some toast as well
console.log("Updates were not cancelled but reload is stopped.")
} else if (error === 'someKnownError') {
// Handle error
} else {
// Log error and/or show a toast message
}
})
} else {
// Perform some action when update is not available
}
} catch (err) {
// Handle error
}
Change the expo-updates package just for your app using a patch
Here you can return a cancel method with Updates.fetchUpdateAsync() and use it with setTimeout to cancel the fetch request. I won't be providing any code for this part but if you are curious I can definitely provide some help.
Please refer this section to understand use of fallbackToCacheTimeout in eas updates.
Old solution:
Now, for aborting or bypassing the promise i.e. Updates.fetchUpdateAsync in your case. You can basically throw an Error in setTimeout after whatever time duration you want, so that, catch block will be executed, bypassing the promises.
Here is the old code :
try{
const update = await Updates.checkForUpdateAsync();
if(update.isAvailable){
// Throw error after 10 seconds.
const timeout = setTimeout(() => { throw Error("Unable to fetch updates. Skipping..") }, 10000)
await Updates.fetchUpdateAsync();
// Just cancel the above timeout so, no error is thrown.
clearTimeout(timeout)
await Updates.reloadAsync();
}else{}
}catch(err){}
I'm having problem to make my Action resolve the promise.
I've read what looks like the most relevant posts.
Returning Promises from Vuex actions
I want to know when my action is finished, then my component can start doing other stuff.
The problem is, the Action never returns the Promise.
myComponent.vue
methods: {
loadUrls() {
this.$store.dispatch('getUrls').then(result => {
console.log("getUrls result", result)
})
},
vuex.js
actions: {
getUrls() {
console.log("getUrls")
return new Promise((resolve) => {
setTimeout(() => {
console.log("setTimeout in")
resolve("Resolved!")
}, 1000)
})
},
That's my console log:
I've used the "setTimeout" to make as simple as possible the problem. In real life I call an API.
I do not need to rely on the result of this promise. I'm aware about it. I use Vuex as the source of truth, but I need to track when the event in completed.
Thanks in advance =)
SOLVED! It worked after I delete my dist Folder, close VSCode and open a new Chrome instance using the new build local host URL.
Thanks #User-28. I saw his shared code and realised nothing was wrong with my code. Then I start looking at my environment.
My very first code didn't have Promise Resolve in the action. I compiled and I was testing it.
Then I found Returning Promises from Vuex actions which explained how to use the Promise in it. I compiled and I was TRYING to test it. Never success. Somehow the code without the Promise was always there. After clean up Dist folder, Close VS code and use a new Chrome instance, the new code was in place and worked.
I'm still don't know the actual problem, but at least it can keep going forward now.
I have a nuxt single page application. The api that I work with has a list of codes for various errors. So, in onError interceptor, the error has to be checked in a dictionary or in a more desired way in a json file. For this, I added a error-handler.js plugin in my nuxt project. But, I don't know how to read from json file.
1) Loading of the json file would occur every time an error thrown?
2) What is the best practice to show the error message to the user? Is this plugin only responsible to create the error-message and in the page try-catch is needed to toast that message?
export default function ({ $axios, store, app, redirect }) {
$axios.onError(error => {
if (error.config.hasOwnProperty('errorHandle') && error.config.errorHandle === false) {
return Promise.reject(error);
}
if (error.message === 'Network Error') {
error.message = 'check the Internet connection';
return
}
const code = parseInt(error.response && error.response.status)
if (error.response)
console.log('error.response', error.response.status, error.response)
if (error.response.data.Errors) {
let errMessage = ''
error.response.data.Errors.forEach(item => {
switch (item.Message.MessageText) {
case 'OrganizationNotFound':
errMessage = 'the organization that you are looking for does not exists'
break
}
})
}
}
}
In Nuxt, plugin code is loaded once or twice per user visit, after that in universal mode it is not executed (of course your onError handler will be). It's once if you make it a client/server-side only plugin, or twice if you need it both on client and server. In your case client-side only plugin sounds like a good choice - just make sure that loading of JSON goes outside of the onError function.
As for how to show it, it depends on your design. We are using Vuetify and have v-snackbar in default layout so it's on every page. Snackbar is bound to VueX value. Then your error plugin can populate that value as appropriate as it will have access to store. This keeps the "raising the error" (dispatch to store) and "showing the error" reasonably decoupled, whilst very reusable (components can also dispatch to store if they face a problem).
I started working with Vuex 2 weeks ago and I realized that Vuex is very good to handle the state of the app. But, it is difficult to handle the error of API calls. When I get data from the server, I dispatch an action. When data is successfully returned, of course, everything is fine. But when an error happens, I change state, I don't know how to detect it through the state from Vuejs components to notify to the user. Could anyone give me some advice?
I typically have the following parts:
A component for displaying the notification, typically an alert or a snackbar or similar, e.g. error-notification. I use this component on a high level, directly below the root app component. This depends on your layout.
A property in vuex indicating the error state, typically an error object w/ error code & message, e.g. error
One mutation in the store for raising an error setting the error property, e.g. raiseError
One mutation in the store for dismissing an error clearing the error property, e.g. dismissError
Using these, you need to:
Display error-notification based on the error in the store: <error-notification v-if="$store.state.error :error="$store.state.error"/>
When an error occurs, call raiseError mutation (in your API callback): vm.$store.commit('raiseError', { code: 'ERR_FOO', msg: 'A foo error ocurred'})
In error-notification, call the dismissError mutation when the notification is closed.
You can also return a promise in your action so that if you call it from component you can catch the error there and display a notification as needed:
in your store:
//action
const fetch = (context) => {
return api.fetchTodos() //api here returns a promise. You can also do new Promise(...)
.then((response) => {
context.commit('SET_TODOS', response);
})
};
in vue component:
this.$store.dispatch('todos/fetch', modifiedTodo)
.catch(error => {
//show notification
})
I'm new to RxJs and Angular2, and I'm trying to properly handle errors. I've seen some examples with Observables that have onNext, onError and onCompleted events (e.g. here, but all of the Angular2 http examples that I see seem to just use .catch and .map methods, and I'm not sure how that relates to the OnNext/OnError/OnCompleted model. I'm working with the code from here):
let stream = this.http.request(options.url, options)
.catch(error: any) => {
this.errorsSubject.next(error);
return Observable.throw(error);
})
.map(this.unwrapHttpValue)
.catch((error: any) => {
return Observable.throw(this.unwrapHttpError(error));
});
I initially wanted to just make it so that the first .catch and the .map are either/or? (i.e. the .map only runs if the http request is successful), but I'm not sure if that's even possible, and then it was further complicated by my reading the post here where it seems like they may be saying that per this fix, the map method will automatically be skipped if the HTTP code is <200 or >300...? However, that isn't what I'm observing in practice with angular 2.0.0-rc.4...
Many thanks for any assistance!
Think of catch being like typical try and catch code. For an observable, all of the operations will be run in order as if they were in a try block. If there is an error, then processing will jump down to the first catch.
So, if you only want to run the map on success, then you just put it before the catch:
let stream = this.http.request(options.url, options)
.map(this.unwrapHttpValue)
.catch(error: any) => {
this.errorsSubject.next(error);
return Observable.throw(error);
});