I am trying to copy a state object:
#boundMethod
private _onClickDeleteAttachment(attachmentName: string): void {
console.log("_onClickDeleteAttachment | this.state.requestApproval[strings.Attachments]: ", this.state.requestApproval[strings.Attachments]);
let requestApprovalClone = {... this.state.requestApproval}
if (requestApprovalClone === this.state.requestApproval) {
console.log("they are ===");
}
else {
console.log(" they are not ===");
}
_.remove(requestApprovalClone[strings.Attachments], (attachment: any) => {
return attachment.FileName === attachmentName;
})
console.log("_onClickDeleteAttachment | this.state.requestApproval[strings.Attachments]: ", this.state.requestApproval[strings.Attachments]);
console.log("_onClickDeleteAttachment | requestApprovalClone[strings.Attachments]: ", requestApprovalClone[strings.Attachments]);
}
The state object is being altered too. From what I have read, I shouldn't mutate a state object but only change it with setState.
How can I correct this?
You are getting that behavior, because the
let requestApprovalClone = {... this.state.requestApproval}
is only shallow copying the data, your attachments property has some nested objects and it keeps the same reference and therefore when changing it, the cloned object gets altered and the state too.
To avoid that, you can perform another copy of your attachments property like this :
let attachments = [...requestApprovalClone[strings.Attachments]];
_.remove(attachments, function (attachment) {
return attachment.FileName === attachmentName;
});
Changing the attachments variable content won't afftect the state anymore.
you can read more about that behavior here
It has to to with the way that JS handles their const references.
For those who feel adventerous:
let requestApprovalClone = JSON.parse(JSON.stringify(this.state.requestApproval));
// modify requestApprovalClone ...
this.setState({
requestApproval:requestApprovalClone
})
It would be interesting if Object.assign({},this.state.requestApproval); is faster than the whole JSON stringify/parse stuff or vice versa
You can have something like:
let requestApprovalClone = Object.assign({},this.state.requestApproval);
requestApprovalClone.strings.Attachments = requestApprovalClone.strings.Attachments.slice(); // will create a shallow copy of this array as well
_.remove(requestApprovalClone[strings.Attachments], (attachment: any) => {
return attachment.FileName === attachmentName;
})
this.setState({
requestApproval:requestApprovalClone
})// If you want to update that in state back
Related
I'm using react native and my component is based on class base function. I'm facing difficulty in updating or adding object in an array..
My case :
I have an array:
this.state = {
dayDeatil:[]
}
now i want to add an obj in it but before that i want check if that object exist or not.
obj = { partition :1, day:"sunday","start_time","close_time",full_day:false}
in condition i will check partition and day if they both not match. then add an object if exist then update.
here is function in which i'm trying to do that thing.
setTimeFunc =(time)=>{
try{
console.log("time.stringify() ")
let obj = {
partition:this.state.activePartition,
day:this.state.selectedDay.name,
full_day:false,
start_time:this.state.key==="start_time"?time.toString():null
close_time:this.state.key==="close_time"?time.toString():null
}
let day = this.state.dayDetails.filter((item)=>item.day===obj.day&&item.partition===obj.partition)
if (day.length!==0) {
day[this.state.key]=time.toString()
this.setState({...this.state.dayDetail,day})
} else {
console.log("2")
this.setState({
dayDetails: [...this.state.dayDetails, obj]
})
}
this.setState({ ...this.state, clockVisiblity: false });
}
catch(e){
console.log("error -> ",e)
}
}
To check if the object exists or not, you can use Array.find() method, if it doesn't exists, the method will return undefined.
Now to update the state, the easier way would be to create a new array and set it as the new dayDetails state like this:
const { dayDetails } = this.state;
dayDetails.push(newData);
this.setState({ dayDetails: [...dayDetails] })
You should use the spread operator when setting the state because React uses shallow comparision when comparing states for a component update, so when you do [...dayDetails] you're creating a new reference for the array that will be on the state, and when React compares the oldArray === newArray, it will change the UI.
Also, after your else statement, you're updating the state with the state itself, it's good to remember that React state updates are asynchronous, so they won't be availabe right after the setState function call, this may be causing you bugs too.
Im using NGRX store on angular project.
This is the state type:
export interface TagsMap {
[key:number]: { // lets call this key - user id.
[key: number]: number // and this key - tag id.
}
}
So for example:
{5: {1: 1, 2: 2}, 6: {3: 3}}
User 5 has tags: 1,2, and user 6 has tag 3.
I have above 200k keys in this state, and would like to make the updates as efficient as possible.
The operation is to add a tag to all the users in the state.
I tried the best practice approach like so :
const addTagToAllUsers = (state, tagIdToAdd) => {
const userIds = Object.keys(state.userTags);
return userIds.reduce((acc, contactId, index) => {
return {
...acc,
[contactId]: {
...acc[contactId],
[tagIdToAdd]: tagIdToAdd
}
};
}, state.userTags);
};
But unfortunately this makes the browser crush when there are over 200k users and around 5 tags each.
I managed to make it work with this:
const addTagToAllUsers = (state, tagIdToAdd) => {
const stateUserTagsShallowCopy = {...state.userTags};
const userIds = Object.keys(stateUserTags);
for (let i = 0; i <= userIds.length - 1; i++) {
const currUserId = userIds[i];
stateUserTagsShallowCopy[currUserId] = {
...stateUserTagsShallowCopy[currUserId],
[tagIdToAdd]: tagIdToAdd
};
}
return stateUserTagsShallowCopy;
};
And the components are updated from the store nicely without any bugs as far as I checked.
But as written here: Redux website mentions :
The key to updating nested data is that every level of nesting must be copied and updated appropriately
Therefore I wonder if my solution is bad.
Questions:
I Believe I'm still shallow coping all levels in state, am i wrong ?
Is it a bad solution? if so what bugs may it produce that I might be missing ?
Why is it required to update sub nested level state in an immutable manner, if the store selector will still fire because the parent reference indeed changed. (Since it works with shallow checks on the top level.)
What is the best efficient solution ?
Regarding question 3, here is an example of the selector code :
import {createFeatureSelector, createSelector, select} from '#ngrx/store';//ngrx version 10.0.0
//The reducer
const reducers = {
userTags: (state, action) => {
//the reducer function..
}
}
//then on app module:
StoreModule.forRoot(reducers)
//The selector :
const stateToUserTags = createSelector(
createFeatureSelector('userTags'),
(userTags) => {
//this will execute whenever userTags state is updated, as long as it passes the shallow check comparison.
//hence the question why is it required to return a new reference to every nested level object of the state...
return userTags;
}
)
//this.store is NGRX: Store<State>
const tags$: Observable<any> = this.store.pipe(select(stateToUser))
//then in component I use it something like this:
<tagsList tags=[tags$ | async]>
</tagsList>
Your solution is perfectly fine.
The rule of thumb is that you cannot mutate an object/array stored in state.
In Your example, the only thing that You are mutating is the stateUserTagsShallowCopy object (it is not stored inside state since it is a shallow copy of state.userTags).
Sidenote: It is better to use for of here since you don't need to access the index
const addTagToAllUsers = (state, tagIdToAdd) => {
const stateUserTagsShallowCopy = {...state.userTags};
const userIds = Object.keys(stateUserTags);
for (let currUserId of userIds) {
stateUserTagsShallowCopy[currUserId] = {
...stateUserTagsShallowCopy[currUserId],
[tagIdToAdd]: tagIdToAdd
};
}
return stateUserTagsShallowCopy;
};
If you decide to use immer this will look like this
import produce from "immer";
const addTagToAllUsers = (state, tagIdToAdd) => {
const updatedStateUserTags = produce(state.userTags, draft => {
for (let draftTags of Object.values(draft)) {
tags[tagIdToAdd] = tagIdToAdd
}
})
return updatedStateUserTags
});
(this comes usually with performance cost). With immer you can sacrifice performance to gain readability
ad 3.
Why is it required to update sub nested level state in an immutable manner, if the store selector will still fire because the parent reference indeed changed. (Since it works with shallow checks on the top level.)
Every store change selectors recompute to see if the dependent component should re-render.
imagine that instead of immutable update of the user tags we decided to mutate tags inside user (state.userTags is a new object reference but we mutate (reuse) old entries objects state.userTags[userId])
const addTagToAllUsers = (state, tagIdToAdd) => {
const stateUserTagsShallowCopy = {...state.userTags};
const userIds = Object.keys(stateUserTags);
for (let currUserId of userIds) {
stateUserTagsShallowCopy[currUserId][tagIdToAdd] = tagIdToAdd;
}
return stateUserTagsShallowCopy;
};
In your case, you have a selector that takes out state.userTags.
It means that every time a state update happens nrgx will compare the previous result of the selector and the current one (prevUserTags === currUserTags by reference). In our case, we change state.userTags so the component that uses this selector will be refreshed with new userTags.
But imagine other selectors that instead of all userTags will select only one user tags. In our imaginary situation, we mutate directly userTags[someUserId] so the reference remains the same each time. The negative effect here is that subscribing component will be not refreshed (will not see an update after a tag is added).
I am struggling to get the real previous state of my inputs.
I think the real issue Which I have figured out while writing this is my use of const inputsCopy = [...inputs] always thinking that this creates a deep copy and i won't mutate the original array.
const [inputs, setInputs] = useState(store.devices)
store.devices looks like this
devices = [{
name: string,
network: string,
checked: boolean,
...etc
}]
I was trying to use a custom hook for getting the previous value after the inputs change.
I am trying to check if the checked value has switched from true/false so i can not run my autosave feature in a useEffect hook.
function usePrevious<T>(value: T): T | undefined {
// The ref object is a generic container whose current property is mutable ...
// ... and can hold any value, similar to an instance property on a class
const ref = useRef<T>();
// Store current value in ref
useEffect(() => {
ref.current = value;
}); // Only re-run if value changes
// Return previous value (happens before update in useEffect above)
return ref.current;
}
I have also tried another custom hook that works like useState but has a third return value for prev state. looked something like this.
const usePrevStateHook = (initial) => {
const [target, setTarget] = useState(initial)
const [prev, setPrev] = useState(initial)
const setPrevValue = (value) => {
if (target !== value){ // I converted them to JSON.stringify() for comparison
setPrev(target)
setTarget(value)
}
}
return [prev, target, setPrevValue]
}
These hooks show the correct prevState after I grab data from the api but any input changes set prev state to the same prop values.
I think my issue lies somewhere with mobx store.devices which i am setting the initial state to or I am having problems not copying/mutating the state somehow.
I have also tried checking what the prevState is in the setState
setInputs(prev => {
console.log(prev)
return inputsCopy
})
After Writing this out I think my issue could be when a value changes on an input and onChange goes to my handleInputChange function I create a copy of the state inputs like
const inputsCopy = [...inputs]
inputsCopy[i][prop] = value
setInputs(inputsCopy)
For some reason I think this creates a deep copy all the time.
I have had hella issues in the past doing this with redux and some other things thinking I am not mutating the original variable.
Cheers to all that reply!
EDIT: Clarification on why I am mutating (not what I intended)
I have a lot of inputs in multiple components for configuring a device settings. The problem is how I setup my onChange functions
<input type="text" value={input.propName} name="propName" onChange={(e) => onInputChange(e, index)} />
const onInputChange = (e, index) => {
const value = e.target.value;
const name = e.target.name;
const inputsCopy = [...inputs]; // problem starts here
inputsCopy[index][name] = value; // Mutated obj!?
setInputs(inputsCopy);
}
that is What I think the source of why my custom prevState hooks are not working. Because I am mutating it.
my AUTOSAVE feature that I want to have the DIFF for to compare prevState with current
const renderCount = useRef(0)
useEffect(() => {
renderCount.current += 1
if (renderCount.current > 1) {
let checked = false
// loop through prevState and currentState for checked value
// if prevState[i].checked !== currentState[i].checked checked = true
if (!checked) {
const autoSave = setTimeout(() => {
// SAVE INPUT DATA TO API
}, 3000)
return () => {
clearTimeout(autoSave)
}
}
}
}, [inputs])
Sorry I had to type this all out from memory. Not at the office.
If I understand your question, you are trying to update state from the previous state value and avoid mutations. const inputsCopy = [...inputs] is only a shallow copy of the array, so the elements still refer back to the previous array.
const inputsCopy = [...inputs] // <-- shallow copy
inputsCopy[i][prop] = value // <-- this is a mutation of the current state!!
setInputs(inputsCopy)
Use a functional state update to access the previous state, and ensure all state, and nested state, is shallow copied in order to avoid the mutations. Use Array.prototype.map to make a shallow copy of the inputs array, using the iterated index to match the specific element you want to update, and then also use the Spread Syntax to make a shallow copy of that element object, then overwrite the [prop] property value.
setInputs(inputs => inputs.map(
(el, index) => index === i
? {
...el,
[prop] = value,
}
: el
);
Though this is a Redux doc, the Immutable Update Patterns documentation is a fantastic explanation and example.
Excerpt:
Updating Nested Objects
The key to updating nested data is that every level of nesting must be
copied and updated appropriately. This is often a difficult concept
for those learning Redux, and there are some specific problems that
frequently occur when trying to update nested objects. These lead to
accidental direct mutation, and should be avoided.
//I want my action to dispatch payload like
// {type:'update',payload:{'current.contact.mobile':'XXXXXXXXX'}}
//In reducer dynamically select the segment of state update needs to be applied to
//Below code doesn't work as expected though, draft always remains at same level
draft = dA.key.split('.').reduce((draft, k) => {
return draft[k]
}, draft);
//Or an ideal syntax may look like below line
draft['current.contact.mobile'] = dA.value;
//Code that works
draft['current']['contact']['mobile'] = dA.value;
I want my action to dispatch payload like
{type:'update',payload:{'current.contact.mobile':'XXXXXXXXX'}}
And in reducer dynamically select the segment of state that needs to be updated.
Is there something fundamentally wrong in doing this, I believe this could make life easier. Is there something that can done to achieve this ?
In your case, this code returns a primitive value like a string or number which is immutable.
draft = dA.key.split('.').reduce((draft, k) => {
return draft[k]
}, draft);
"Immer" is using Proxy to implement all this magic. The proxy could work only on objects for example Object, Array, Function etc.
so to fix your problem you can use code like this
import produce from "immer";
describe("Why immer.js doesn't allow setting dynamic properties on draft?", function() {
it("should allow set dynamic properties", function() {
const path = "foo.bar.zoo";
const state = { foo: { bar: { zoo: 1 } } };
const nextState = produce(state, draft => {
const vector = path.split(".");
const propName = vector.pop();
if (propName) {
draft = vector.reduce((it, prop) => it[prop], draft);
draft[propName] += 1;
}
});
expect(nextState.foo.bar.zoo).toEqual(state.foo.bar.zoo + 1);
});
});
In the code above, we get destination object and update the property of this object.
Some note about string and number.
Javascript has constructors for string and number which return objects not primitive values. But this is a very rare case when someone uses it explicitly.
Usually, we deal with it implicitly when writing something like this dA.key.split('.'). In this case, the interpreter would create a string object and call method "split" on it. Usually, this behavior is referred to as "Boxing"
Simple: the computed value isn't updating when the observable it references changes.
import {observable,computed,action} from 'mobx';
export default class anObject {
// THESE WRITTEN CHARACTERISTICS ARE MANDATORY
#observable attributes = {}; // {attribute : [values]}
#observable attributeOrder = {}; // {attribute: order-index}
#observable attributeToggle = {}; // {attribute : bool}
#computed get orderedAttributeKeys() {
const orderedAttributeKeys = [];
Object.entries(this.attributeOrder).forEach(
([attrName, index]) => orderedAttributeKeys[index] = attrName
);
return orderedAttributeKeys;
};
changeAttribute = (existingAttr, newAttr) => {
this.attributes[newAttr] = this.attributes[existingAttr].slice(0);
delete this.attributes[existingAttr];
this.attributeOrder[newAttr] = this.attributeOrder[existingAttr];
delete this.attributeOrder[existingAttr];
this.attributeToggle[newAttr] = this.attributeToggle[existingAttr];
delete this.attributeToggle[existingAttr];
console.log(this.orderedAttributeKeys)
};
}
After calling changeAttribute, this.orderedAttributeKeys does not return a new value. The node appears unchanged.
However, if I remove the #computed and make it a normal (non-getter) function, then for some reason this.orderedAttributeKeys does display the new values. Why is this?
EDIT: ADDED MORE INFORMATION
It updates judging by logs and debugging tools, but doesn't render on the screen (the below component has this code, but does NOT re-render). Why?
{/* ATTRIBUTES */}
<div>
<h5>Attributes</h5>
{
this.props.appStore.repo.canvas.pointerToObjectAboveInCanvas.orderedAttributeKeys.map((attr) => { return <Attribute node={node} attribute={attr} key={attr}/>})
}
</div>
pointerToObjectAboveInCanvas is a variable. It's been set to point to the object above.
The changeAttribute function in anObject is called in this pattern. It starts in the Attribute component with this method
handleAttrKeyChange = async (existingKey, newKey) => {
await this.canvas.updateNodeAttrKey(this.props.node, existingKey, newKey);
this.setState({attributeEdit: false}); // The Attribute component re-renders (we change from an Input holding the attribute prop, to a div. But the above component which calls Attribute doesn't re-render, so the attribute prop is the same
};
which calls this method in another object (this.canvas)
updateNodeAttrKey = (node, existingKey, newKey) => {
if (existingKey === newKey) { return { success: true } }
else if (newKey === "") { return { success: false, errors: [{msg: "If you'd like to delete this attribute, click on the red cross to the right!"}] } }
node.changeAttribute(existingKey, newKey);
return { success: true }
};
Why isn't the component that holds Attribute re-rendering? It's calling orderedAttributeKeys!!! Or am I asking the wrong question, and something else is the issue...
An interesting fact is this same set of calls happens for changing the attributeValue (attribute is the key in anObject's observable dictionary, attributeValue is the value), BUT it shows up (because the Attribute component re-renders and it pulls directly from the node's attribute dictionary to extract the values. Again, this is the issue, an attribute key changes but the component outside it doesn't re-render so the attribute prop doesn't change?!!!
It is because you have decorated changeAttribute with the #action decorator.
This means that all observable mutations within that function occur in a single transaction - e.g. after the console log.
If you remove the #action decorator you should see that those observables get updated on the line they are called and your console log should be as you expect it.
Further reading:
https://mobx.js.org/refguide/action.html
https://mobx.js.org/refguide/transaction.html
Try to simplify your code:
#computed
get orderedAttributeKeys() {
const orderedAttributeKeys = [];
Object.entries(this.attributeOrder).forEach(
([attrName, index]) => orderedAttributeKeys[index] = this.attributes[attrName])
);
return orderedAttributeKeys;
};
#action.bound
changeAttribute(existingAttr, newAttr) {
// ...
};
Also rename your Store name, Object is reserved export default class StoreName