I am quite new to Vue.js and while developing my first project i have stumbled upon a problem which I think is related to the component's lifecycle.
The context is the following:
I am using Vue 3 with composition API.
I have a "Map" component in which I use d3.js to show a chart.
In my Setup() method I have onBeforeMount() and onMounted().
In onBeforeMount() method, I want to use data from my Firestore database for the values in the chart. The console.log on line 47 shows the data correctly.
In onMounted(), is where I plan to put my d3 chart. But when I try to access the data as in console.log on line 55, I get undefined...
Ideally, from "Map" component, I want to fetch the data from my database and use it in order to create the chart and then have the component render the chart.
Then I would have another component called 'MapSettings" that will be able to alter the data in "Map" such as filters etc...and have the values automatically updated in the chart.
Finally, both components will be siblings and have same parent component. So "Map" and "MapSettings" are on same hierarchical level.
But first I need to understand why I am getting undefined.. Any help or suggestion would be greatly appreciated!
Your lifecycle hooks look nice. The problem that you're facing has to do with code been executed asynchronously and code been executed synchronously.
You're declaring a function that uses async-await feature. This function will be executed asynchronously. In this case, you're getting data from Firestore and storing it in a ref at onBeforeMount().
On the other hand, you're declaring a normal function at onMounted() trying to access a ref's value, which will result in undefined because the function that you define at onBeforeMount() didn't finish its execution (or it's in the event queue) when onMounted is called.
That's why you first see the console.log that comes from onMounted.
One solution would merge both functions in one lifecycle hooks and use async await:
setup() {
const {actorDocs, load} = getActorDocs()
const actorsData = red([])
// load actor data from db
onBeforeMount( async () => {
await load()
actorsData.value = actorDocs
console.log(actorsData.value)
// manipulate it here...
})
}
Keep in mind that you cannot pause with async-await a lifecycle hook. What you're pausing is the function that Vue will execute in that hook. Indeed, this is really nice because pausing a hook wouldn't be efficient at all.
i face that problem, in my case i want use imgsRef.value out of onBeforeMount scope. How to get imgsRef value out of beforeMount scope?
onBeforeMount( async () => {
await axios
.get("http://localhost:3000/ourMoment")
.then((response) => {
imgsRef.value = response.data
// imhsRef get the value from api
console.log(imgsRef.value.photo)
})
})
// i try to concole.log here but the value still empty
console.log(imgsRef.value)
Related
I'm working on my first Vue 3 (and therefore vuex 4) app coming from a pretty solid Vue 2 background.
I have an component that is loading data via vuex actions, and then accessing the store via a returned value in setup()
setup() {
const store = useStore();
const fancy = computed(() => store.state.fancy);
return { fancy };
},
fancy here is a deeply nested object, which I think might be important.
I then want to run a function based on whenever than value changes, so I have set up a watch in my mounted() lifecycle hook
watch(
this.fancy,
(newValue) => {
for (const spreadsheet in newValue) {
console.log(Object.keys(newValue[spreadsheet].data))
setTimeout(()=>{
console.log(Object.keys(newValue[spreadsheet].data))
},500)
...
I tried using the new onMounted() hook in setup and watchEffect and store.watch instead, but I could not get watch/watchEffect to reliably trigger in the onMounted hook, and watchEffect never seemed to update based on my computed store value. If you have insight into this, that would be handy.
My real issue though is that my watcher gets called seemingly before the value is updated. For instance my code logs out [] for the first set of keys, and then a half second later a full array. If it was some kind of progressive filling in of the data, then I would have expected the watcher to be called again, with a new newValue. I have also tried. all the permutations of flush, deep, and immediate on my watcher to no avail. nextTick()s also did not work. I think this must be related to my lack of understanding in the new reactivity changes, but I'm unsure how to get around it and adding in a random delay in my app seems obviously wrong.
Thank you.
I have a call in my created method which has an await.
I want to know that the results of that call are loaded so that i can conditionally show/hide things in the DOM.
Right now it looks like the DOM is being rendered before that method has completed. But I though that methods in created were called before the DOM rendered?
You're correct in assuming that the created hook runs before the component mounts. However, the lifecycle hooks are not waiting for async calls to complete. If you want to wait for that call to be completed and data to load, you can do so by using a Boolean that you set to true when your data has loaded.
Your template:
<div v-if='dataLoaded'>Now you can see me.</div>
in your vue instace
export default {
data () {
return {
dataLoaded: false
}
},
created () {
loadMyData().then(data => {
// do awesome things with data
this.dataLoaded = true
})
}
}
This way you can keep your content hidden until that call has resolved. Take care with the context when you handle the ajax response. You will want to keep this as a reference to the original vue instance, so that you can set your data correctly. Arrow functions work well for that.
I am trying to get all of the Vue components data properties from within a mixin that I am using for my plugin.
I have got the plugin registering correctly and the mixin is actively working.
I have added a lifecycle hook from within the Vue.mixin which runs on the created() event.
I am trying to loop through all of the components data and assign it to a property within my plugin, this is because I want to manipulate all of the data in every single component in my application.
I have tried to do the following:
Vue.mixin({
created() {
console.log(this.$options.data());
}
})
But i get the result saying that data is not a function. However, calling within the () on the end of the data logs a function out which I can see the data within.
Does anyone have any ideas?
Thank you
Try to use this.$data instead:
Vue.mixin({
created() {
console.log(this.$data);
}
});
>> DEMO on CodeSandbox
EDIT AGAIN: Opened an issue with Reflux here: https://github.com/reflux/refluxjs/issues/544
EDIT: Reflux setState does not provide any callback for setState. They require you to use the component lifecycle methods to ensure the state is set prior to running any code. If you ever need to use the reflux setState outside of a component, where you do not have lifecycle methods, you will not be guaranteed the state is set. This is due to how Reflux does their setState. It loops all listening components and calls those components' setState methods. If Reflux were refactored to wait until all the listening components' setState calls complete then call a callback passed into its own setState method, that may work, but it would likely require a large rework of Reflux. I have started using a singleton class to manage some of these variables, as they are fully outside the component lifecycle.
Can you use setState with a callback in ReactNative or is that only in React? I'm using the below syntax and the first debugger is hit, but the second debugger and console log never get hit.
EDIT: After digging some more, it seems this does not occur when using setting the state directly, but only when running it through a reflux store and/or not using a component.
See snack here: https://snack.expo.io/S1dm3eFoM
debugger
this.setState(
params,
() => {
debugger
console.log("CALLIN IT BACK")
}
)
I'm the creator of Reflux's ES6 styled stores/component hookups. Hopefully I can shed some light on this for you.
Here's the important points:
1) Reflux sets its store state immediately upon setState calls.
Reflux's store state doesn't have the same problems as React and doesn't need React's workaround (callback). You are guaranteed that your change is immediately reflected in the store's state, that's why there is not a callback. The very next line of code will reflect the store's new state.
tl;dr, no workaround is required.
// in Reflux stores this works
this.setState({foo:'foo'});
console.log(this.state.foo === 'foo') // true
this.setState({foo:'bar'});
console.log(this.state.foo === 'bar') // true
2) Stores can never depend upon components!
The idea that the setState would give a callback about when the dependent components have all updated their state is a major violation of the single most fundamental of all flux principles: 1 way data flow.
If your store requires knowledge about whether or not components are doing something then you are already doing it wrong, and all the problems you are experiencing are XY problems of fundamentally not following flux in the first place. 1-way data flow is a main flux principle.
And that principle exists for good reason. Flux doesn't require 1:1 mapping of store state properties to component state properties. You can map anything to anything, or even just use the store's state for the building blocks of how you will run your own logic to create completely new state properties on the components. For example having loaded and transitioned as separate properties in store state, but mapping to a loadedAndTransitioned property in one component, and a notLoadedOrTransitioned in another component via your own custom logic. That's a hugely powerful part of flux. But your suggestion would pretty much destroy all that, since Reflux can't map people's custom logic.
1-way data flow must be maintained; Store's must operate the same independently of what components utilize them. Without this, the power of flux falls apart!
Store's listen to actions, components listen to stores, actions are called from wherever. All flux-based data flows from action -> store -> component only.
I've checked the library for the refluxjs and the problem and the workaround are as mentioned below.
Problem
The library provides with a new instance of the setState which is not exactly similar to ReactJS setState, which omits the callback as mentioned in their code below.
/dist/reflux.js
proto.setState = function (obj) {
// Object.assign(this.state, obj); // later turn this to Object.assign and remove loop once support is good enough
for (var key in obj) {
this.state[key] = obj[key];
}
// if there's an id (i.e. it's being tracked by the global state) then make sure to update the global state
if (this.id) {
Reflux.GlobalState[this.id] = this.state;
}
// trigger, because any component it's attached to is listening and will merge the store state into its own on a store trigger
this.trigger(obj);
};
Also as mentioned here in the docs
That store will store its state on a this.state property, and mutate its state via this.setState() in a way that is extremely similar to React classes themselves.
WorkAround
The library provides with the listener functions, which provide us with the callbacks of the setState obj of the ReactJS as mentioned in the below snippet.
/dist/reflux.js
componentDidMount: function() {
var me = this;
_.extend(me, ListenerMethods);
this.listenTo(listenable, function(v) {
me.setState(_.object([key],[v]));
});
},
You can use them in the following way
this.listenTo(action, callback)
Hope it clears the doubts
Edit:
Usage as per the docs
To listen inside of the store
constructor()
{
super();
this.state = {count: 0};
this.listenTo(increment, this.incrementItUp);
}
incrementItUp()
{
var newCount = this.state.count + 1;
this.setState({count: newCount});
}
To listen outside of the store anywhere
// listen directly to an action
myActions.actionName.listen(myCallbackFunc);
// listen to a child action
myActions.load.completed.listen(myCallbackFunc);
Here's the link to the snack with working callbacks based on Promises
I have a component whose data is initialized by ajax. I know vue.js has provide several lifecycle hooks: Lifecycle-Diagram. But for ajax to initialize the data, which hook(beforeCreate, create, mounted, etc) is the best place to do it:
hook_name: function() {
ajaxCall(function(data) {
me.data = data;
});
}
Currently, i do it in mounted, making it to re-render the component. But i think we should get the data before the first render. Can someone figure out the best way to do it?
If you want to initialize your component with data you receive from a request, created() would be the most appropriate hook to use but it is a request, it might not resolve by the end of created or even mounted() (when even your DOM is ready to show content!).
So do have your component initialized with empty data like:
data () {
return {
listOfItems: [],
someKindOfConfig: {},
orSomeSpecialValue: null
}
}
and assign the actual values when you receive them in your created hook as these empty data properties would be available at that point of time, like:
created () {
someAPICall()
.then(data => {
this.listOfItems = data.listOfItems
})
/**
* Notice the use of arrow functions, without those [this] would
* not have the context of the component.
*/
}
It seems like you aren't using (or aren't planning to use) vuex but I'd highly recommend you to use it for for managing your data in stores. If you use vuex you can have actions which can make these api calls and by using simple getters in your component you would have access to the values returned by the request.