I want to know what does ...state inside { ...state } do? Is it to change the value of the store to the initial value or to let the store be the latest value?
import * as actionType from "../actions/actionTypes";
const initialStore = {
roomsCount: 0,
resPerPage: 0,
rooms: [],
filteredRooms: 0,
error: null,
success: false,
};
const reducer = (state = initialStore, action) => {
switch (action.type) {
case actionType.ALL_ROOM_SUCCESS:
return {
...state,
success: true,
rooms: action.rooms,
roomsCount: action.roomsCount,
resPerPage: action.resPerPage,
filteredRooms: action.filteredRooms,
};
case actionType.ALL_ROOM_FAILED:
return {
...state,
error: action.err,
};
}
};
If at first I use this reducer, it'll be successful so success will be true and error will be null. But if it fails the 2nd time and I use ...state in this situation, what is the success value? Is it the initial value (false) or does it keep the value from the first request (true)?
That is called the spread operator and it basically allows you to "clone" the fields of one object into a new object.
In your example, { ...state, error: action.err } means "copy all fields from state, but set the field error to action.err". It's very handy for this kind of logic where you want to change a very few fields but otherwise want to keep the original data.
Related
I have a problem with my code. I currently have some data like the one below;
users: [
{
name: 'bolu',
features: ['Tall'],
},
{
name: 'cam',
features: ['Bearded', 'Short'],
},
],
};
What I am trying to do is delete/remove a single feature - for example if I pass in 'short' into my redux action. I'd like for it (the 'Short' text) to be removed from the features array. I currently have my redux action set up this way:
export interface UsersDataState {
name: string,
features: Array<string>,
}
export interface UsersState {
users: UsersDataState[];
}
const initialState: UsersState = {
users: [],
};
export const usersSlice = createSlice({
name: 'users',
initialState,
reducers: {
removeUser: (state, action: PayloadAction<string>) => {
const removedUsers = state.users.filter((user) => user.features.indexOf(action.payload));
state.users = removedUsers;
},
},
});
So here I am passing in the value in (action.payload is the value being passed in). When this action is dispatched, I want to remove just the word that is passed in from the features array. I hope this is clearer now.
This doesn't work for some reason and I am unable to figure out why. Any help would be appreciated please, thank you.
Your code doesn't match your state structure. Replace traits with users, and values with features.
It looks like that's a part of a reducer, not an action (which is an object, not a function).
You should be returning a new state from the reducer.
Given your update the function should be called removeFeature.
So, I've corrected a few bits of your code based on what I remember from Redux. Note: contrived example.
// State
const state={users:[{name:"joe",features:["Mean","Short"]},{name:"bolu",features:["Tall"]},{name:"cam",features:["Bearded","Short"]}]};
// The reducer accepts a state, and an action
function reducer(state, action) {
// We destructure the type, and payload, from the action object
const { type, payload } = action;
// Depending on the type...
switch (type) {
case 'removeFeature': {
// `map` over the users (we return a new state array)
return state.users.map(user => {
// `filter` out the feature elements
// that match the payload
const updatedFeatures = user.features.filter(feature => {
return feature !== payload;
});
// Return a new updated object
return { ...user, features: updatedFeatures };
});
}
default: return state;
}
}
const updatedState = reducer(state, {
type: 'removeFeature',
payload: 'Short'
});
console.log(updatedState);
In Javascript, string, integer and boolean values are immutable, but objects and arrays are mutable.
How should we update states in React, if states have both types of values?
e.g.
constructor(props) {
super(props);
this.state = {
success: false,
error: false,
errorMessages: {}
};
}
Assuming that you need to upgdate all of the properties (success, error, errorMessages) at once, what would be best way to achieve it?
At least I'm sure that errorMessages shouldn't be updated directly, because it's mutable by nature, but what about the rest of them?
I tried something like the following, but this ends up in a wrong result.
const errorMessages = {
...this.state,
"errorMessages": error.response.data,
};
this.setState({
errorMessages,
success: false,
error: true,
});
//The errorMessages property will have "success" and "error" property in it
As long as you supply a new value for errorMessages, React will update the state correctly. You're not mutating state directly here, you're just providing a new value for the field, and React will do the necessary mutation:
this.setState({
errorMessages: error.response.data
success: false,
error: true,
});
So assuming your state is originally this
this.state = {
success: false,
error: false,
errorMessages: {}
};
And then you create a new object for your errorMessages like this
const errorMessages = {
...this.state,
"errorMessages": error.response.data,
};
this.setState({
errorMessages,
success: false,
error: true,
});
Then, your next state will kinda look like this, and I am unsure if this is what you want
{
errorMesages: {
success: false,
error: true,
errorMessages: {
// content of the error.response.data
}
},
success: false,
error: true
}
You probably wanted to assign the new state directly, which is in fact the errorMessages const you created, you are just over doing it ;)
The reason why this is so, is because when adding a variable to an object without a value, but just by name, javascript will automatically name the label the same as the variable, eg:
const a = 10;
const b = {
a
};
// result in: { a: 10 };
console.log(b);
There are 3 ways to update state:
this.setState({
success: !this.state.success,
error: !this.state.error,
errorMessages: delete this.state.id // if id were a prop in errorMessages
})
this.setState((prevState) => {
return {
success: !prevState.success,
error: !prevState.error,
errorMessages
}
});
this.setState((prevState) => {
return {
success: !prevState.success,
error: !prevState.error,
errorMessages
}
}, () => { // some callback function to execute after setState completes })
I am trying to fetch a new batch of products through an action and then replace the state with the new batch, however it just adds it to the array...
Here's my reducer for controlling the state:
const initialState = {
fetching: false,
fetched: false,
Brands:[],
Markings:[],
Products: [],
error: null
}
export default function reducer(state=initialState, action=null) {
switch (action.type){
case "FETCH_PRODUCTS_PENDING" : {
return {...state}
break;
}
case "FETCH_PRODUCTS_REJECTED" : {
return {...state}
break;
}
case "FETCH_PRODUCTS_FULFILLED" : {
return{ ...state,
Products: state.Products.concat(action.payload.data.Products),
Brands: action.payload.data.Facets[0].Facets,
Markings: action.payload.data.Facets[1].Facets
}
break;
}
}
return state
}
It goes wrong in the fulfilled case.. I am not sure how this "...state" works, do I need to do a object assign or something?
Upon load I get 52 products, when trying to request a new batch it adds it up so my this.props.products is 104 items... I want it to replace
This line is the culprit
Products: state.Products.concat(action.payload.data.Products),
In this case all you want to do is replace the Products array with the one from the action.
So it should be simply
Products: action.payload.data.Products
See here for a nice explanation on the spread operator:
https://ponyfoo.com/articles/es6-spread-and-butter-in-depth
Below is my code
function customMsg(state, action) {
state = state || {
person: {
isFetching: false,
didInvalidate: false,
name: "",
height: "",
}
};
switch(action.type) {
case ACTION_TYPES.PERSON.FETCH_PERSOn_CONTENT_SUCCESS:
return $.extend({}, state, {
person.name: action.result.name
});
default:
return state;
}
}
How do I only update one value of my reducer in Redux?
Above is a example which i only want to update the name of person object.
How can i do that?
Using jQuery extend, create a clone and set person name:
var newState = $.extend({}, state);
newState.person.name = action.result.name;
return newState;
Otherwise, to clone deeply an object you can use lodash cloneDeep().
Another way is to use immutableJS to set your app state as immutable. It is much more bug "mutable" proof and offers functions to set deep nested value in an immutable. See updateIn:
return state.updateIn(['person', 'name'], () => action.result.name);
Try it!
I have an issue where re-rendering of state causes ui issues and was suggested to only update specific value inside my reducer to reduce amount of re-rendering on a page.
this is example of my state
{
name: "some name",
subtitle: "some subtitle",
contents: [
{title: "some title", text: "some text"},
{title: "some other title", text: "some other text"}
]
}
and I am currently updating it like this
case 'SOME_ACTION':
return { ...state, contents: action.payload }
where action.payload is a whole array containing new values. But now I actually just need to update text of second item in contents array, and something like this doesn't work
case 'SOME_ACTION':
return { ...state, contents[1].text: action.payload }
where action.payload is now a text I need for update.
You can use map. Here is an example implementation:
case 'SOME_ACTION':
return {
...state,
contents: state.contents.map(
(content, i) => i === 1 ? {...content, text: action.payload}
: content
)
}
You could use the React Immutability helpers
import update from 'react-addons-update';
// ...
case 'SOME_ACTION':
return update(state, {
contents: {
1: {
text: {$set: action.payload}
}
}
});
Although I would imagine you'd probably be doing something more like this?
case 'SOME_ACTION':
return update(state, {
contents: {
[action.id]: {
text: {$set: action.payload}
}
}
});
Very late to the party but here is a generic solution that works with every index value.
You create and spread a new array from the old array up to the index you want to change.
Add the data you want.
Create and spread a new array from the index you wanted to change to the end of the array
let index=1;// probably action.payload.id
case 'SOME_ACTION':
return {
...state,
contents: [
...state.contents.slice(0,index),
{title: "some other title", text: "some other text"},
...state.contents.slice(index+1)
]
}
Update:
I have made a small module to simplify the code, so you just need to call a function:
case 'SOME_ACTION':
return {
...state,
contents: insertIntoArray(state.contents,index, {title: "some title", text: "some text"})
}
For more examples, take a look at the repository
function signature:
insertIntoArray(originalArray,insertionIndex,newData)
Edit:
There is also Immer.js library which works with all kinds of values, and they can also be deeply nested.
You don't have to do everything in one line:
case 'SOME_ACTION': {
const newState = { ...state };
newState.contents =
[
newState.contents[0],
{title: newState.contents[1].title, text: action.payload}
];
return newState
};
I believe when you need this kinds of operations on your Redux state the spread operator is your friend and this principal applies for all children.
Let's pretend this is your state:
const state = {
houses: {
gryffindor: {
points: 15
},
ravenclaw: {
points: 18
},
hufflepuff: {
points: 7
},
slytherin: {
points: 5
}
}
}
And you want to add 3 points to Ravenclaw
const key = "ravenclaw";
return {
...state, // copy state
houses: {
...state.houses, // copy houses
[key]: { // update one specific house (using Computed Property syntax)
...state.houses[key], // copy that specific house's properties
points: state.houses[key].points + 3 // update its `points` property
}
}
}
By using the spread operator you can update only the new state leaving everything else intact.
Example taken from this amazing article, you can find almost every possible option with great examples.
This is remarkably easy in redux-toolkit, it uses Immer to help you write immutable code that looks like mutable which is more concise and easier to read.
// it looks like the state is mutated, but under the hood Immer keeps track of
// every changes and create a new state for you
state.x = newValue;
So instead of having to use spread operator in normal redux reducer
return {
...state,
contents: state.contents.map(
(content, i) => i === 1 ? {...content, text: action.payload}
: content
)
}
You can simply reassign the local value and let Immer handle the rest for you:
state.contents[1].text = action.payload;
Live Demo
In my case I did something like this, based on Luis's answer:
// ...State object...
userInfo = {
name: '...',
...
}
// ...Reducer's code...
case CHANGED_INFO:
return {
...state,
userInfo: {
...state.userInfo,
// I'm sending the arguments like this: changeInfo({ id: e.target.id, value: e.target.value }) and use them as below in reducer!
[action.data.id]: action.data.value,
},
};
Immer.js (an amazing react/rn/redux friendly package) solves this very efficiently. A redux store is made up of immutable data - immer allows you to update the stored data cleanly coding as though the data were not immutable.
Here is the example from their documentation for redux:
(Notice the produce() wrapped around the method. That's really the only change in your reducer setup.)
import produce from "immer"
// Reducer with initial state
const INITIAL_STATE = [
/* bunch of todos */
]
const todosReducer = produce((draft, action) => {
switch (action.type) {
case "toggle":
const todo = draft.find(todo => todo.id === action.id)
todo.done = !todo.done
break
case "add":
draft.push({
id: action.id,
title: "A new todo",
done: false
})
break
default:
break
}
})
(Someone else mentioned immer as a side effect of redux-toolkit, but you should use immer directly in your reducer.)
Immer installation:
https://immerjs.github.io/immer/installation
This is how I did it for one of my projects:
const markdownSaveActionCreator = (newMarkdownLocation, newMarkdownToSave) => ({
type: MARKDOWN_SAVE,
saveLocation: newMarkdownLocation,
savedMarkdownInLocation: newMarkdownToSave
});
const markdownSaveReducer = (state = MARKDOWN_SAVED_ARRAY_DEFAULT, action) => {
let objTemp = {
saveLocation: action.saveLocation,
savedMarkdownInLocation: action.savedMarkdownInLocation
};
switch(action.type) {
case MARKDOWN_SAVE:
return(
state.map(i => {
if (i.saveLocation === objTemp.saveLocation) {
return Object.assign({}, i, objTemp);
}
return i;
})
);
default:
return state;
}
};
I'm afraid that using map() method of an array may be expensive since entire array is to be iterated. Instead, I combine a new array that consists of three parts:
head - items before the modified item
the modified item
tail - items after the modified item
Here the example I've used in my code (NgRx, yet the machanism is the same for other Redux implementations):
// toggle done property: true to false, or false to true
function (state, action) {
const todos = state.todos;
const todoIdx = todos.findIndex(t => t.id === action.id);
const todoObj = todos[todoIdx];
const newTodoObj = { ...todoObj, done: !todoObj.done };
const head = todos.slice(0, todoIdx - 1);
const tail = todos.slice(todoIdx + 1);
const newTodos = [...head, newTodoObj, ...tail];
}
Pay attention to the data structure:
in a project I have data like this
state:{comments:{items:[{...},{...},{...},...]} and to update one item in items I do this
case actionTypes.UPDATE_COMMENT:
const indexComment = state.comments.items.findIndex(
(comment) => comment.id === action.payload.data.id,
);
return {
...state,
comments: {
...state.comments,
items: state.comments.items.map((el, index) =>
index === indexComment ? { ...el, ...action.payload.data } : el,
),
},
};
Note: in newer versions (#reduxjs/toolkit), Redux automatically detects changes in object, and you don't need to return a complete state :
/* reducer */
const slice = createSlice({
name: 'yourweirdobject',
initialState: { ... },
reducers: {
updateText(state, action) {
// updating one property will cause Redux to update views
// only depending on that property.
state.contents[action.payload.id].text = action.payload.text
},
...
}
})
/* store */
export const store = configureStore({
reducer: {
yourweirdobject: slice.reducer
}
})
This is how you should do now.