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How do i fetch json from a url and display json content on my js page

Im making a custom MS Teams app and in the app im trying to fetch a json from a url to then display the contents later. However, the fetch is failing. My goal is to fetch a list of data from a supplied url and then displaying it in the Tab within my teams app, which would be here: Where i want my json content to show up
As you can probably tell, i dont have any experience with javascript at all, but the custom MS teams app wants javascript...
// Copyright (c) Microsoft Corporation. All rights reserved.
// Licensed under the MIT License.
import React from 'react';
import './App.css';
import * as microsoftTeams from "#microsoft/teams-js";
/**
* The 'GroupTab' component renders the main tab content
* of your app.
*/
class Tab extends React.Component {
constructor(props){
super(props)
this.state = {
context: {}
}
}
//React lifecycle method that gets called once a component has finished mounting
//Learn more: https://reactjs.org/docs/react-component.html#componentdidmount
componentDidMount(){
// Get the user context from Teams and set it in the state
microsoftTeams.getContext((context, error) => {
this.setState({
context: context
});
});
// Next steps: Error handling using the error object
}
componentDidMount() {
fetch('http://example.com/movies.json')
.then(response => response.json())
.then(data => console.log(data));
}
render() {
var jsondata = data;
let userName = Object.keys(this.state.context).length > 0 ? this.state.context['upn'] : "";
return (
<div>
</div>
);
}
}
export default Tab;
So to sum it all up, how do i fetch my json from a url and display the content of that json on my tab.js page within teams?
Thanks in advance for any help.

While I can't speak to how the Teams API works, I can help you understand how to render things from a json API in your react component.
In your componentDidMount function, your example is sending and receiving the response from the API. To render this response, we need to assign the data to your component's "state" and then use that to render it in HTML.
This will be pretty simple. First, you need to extend your component's state, in a similar manner as you've done for context. Do this first in the constructor, where we'll declare an initial state of an empty object (I'll name it content but you can use whatever name makes most sense):
// inside the constructor() function
this.state = {
context: {},
content: {}
}
In React, we use setState to update this state object state when something changes, like on a lifecycle method such as componentDidMount. You just need to call this setState again when you want to change the state object from its initial value to something else. In our case, when we receive the data from the API.
setState takes whatever you provide it and merges it into the state object, so you only should declare anything you want to change. Anything else not declared will remain unchanged.
So, in componentDidMount, we can make a small change to do something with data when it arrives:
componentDidMount() {
fetch('http://example.com/movies.json')
.then(response => response.json())
.then(data => {
this.setState({
content: data
})
});
}
This is basically saying:
once the component has mounted, make a call to fetch from the API
then, with that response, take the json from the body
and then, assign the json "data" into our component's state object under the key of content.
You can then do things with this data by calling this.state.content. I'm not sure what format the data will come in, but whatever json object arrives back from the API will be stored under this.state.content.
As an example, imagine we get a simple object back from the API that looks like this { title: "Tab title" }. It means that, on a successful call to the API, our state object will look like this:
{
context: "whatever you have here", // whatever you have here, I don't know this
content: { title: "Tab title" }
}
When this state object is updated, react will trigger a new render of the component.
So, to make it appear in our component, we need to use this state in our render function (we wrap things in curly braces if they need to be dynamically rendered rather than hardcoded):
render() {
return (
//... the rest of your function
<div>{this.state.content.title}</div>
);
}
As you might have guessed, this will show the title inside a div, if the title exists.
Eventually, you should consider handling the state of the component before that API call has resolved itself. The lifecycle method componentDidMount will be called after the component is mounted, and because you're hitting an API, there will be something rendered to the DOM before the API call resolves itself. In my example, it'll be just be an empty div, and then it'll appear when the state updates and the render function is called again.
You could do this more effectively by extending your state object to see whether the API response is done (you'd update this in the same place you set the content), and you could render the UI conditionally on this.
The official docs on lifecycle methods will help you understand this pattern more.
Good luck!

Well, you can rely on #Josh Vince for an explanation as he did it perfectly, I will just write the code a bit cleaner for you.
Let's create 2 methods that will set the state with respective data and then simply call the state values and render the following as per your wish.
import React, {Component} from 'react';
import './App.css';
import * as microsoftTeams from "#microsoft/teams-js";
class Tab extends Component {
this.state = {
context: {},
movies: null
}
getContext = () => {
try {
microsoftTeams.getContext((context) => this.setState({context}));
}
catch(error){
console.log('ERROR ->', error);
throw error;
}
}
fetchMoviesData = () => {
try {
fetch('http://example.com/movies.json')
.then(response => response.json())
.then(data => this.setState({movies: data}));
} catch(error){
console.log('ERROR ->', error);
throw error;
}
}
componentDidMount() {
this.getContext();
this.fetchMoviesData();
}
render() {
let {movies, context} = this.state;
const jsondata = movies;
let userName = Object.keys(this.state.context).length ? context['upn'] : "";
return <>JSONDATA: {jsondata}, USERNAME: {userName}</>
}
}
export default Tab;

React functional component is taking snapshot of state at the time of registering handler on websocket

react functional component is taking snapshot of state at the time of subscription.
For ex. PFB code.
If i click setSocketHandler button and then press setWelcomeString button. Now if i receive message over socket when i log welcomestring it is empty.
But if i click setWelcomeString button and then click setSocketHandler button. Now if i receive message on socket Welcome is getting logged on console.
I have seen same behaviour in project so just created this simple app to prove.
If i use class component which is commented below.. everything works fine.
So my question is why react functional component is working on a state at the time of reg and not on actual state at the time message is received.
This is very weird. How to make it work in functional component correctly.
import React, {useEffect, useState} from 'react';
import logo from './logo.svg';
import './App.css';
const io = require('socket.io-client');
const socket = io.connect('http://localhost:3000/');
const App : React.FunctionComponent = () => {
const [welcomeString, setWelcomeString] = useState("");
const buttonCliecked = () => {
console.log("clocked button");
setWelcomeString("Welcome")
}
const onsockethandlerclicked = () => {
console.log("socket handler clicked");
socket.on('out', () => {
console.log("Recived message")
console.log(welcomeString);
});
}
return (
<div>
<header className="component-header">User Registration</header>
<label>{welcomeString}</label>
<button onClick={buttonCliecked}>setWelcomeString</button>
<button onClick={onsockethandlerclicked}>setSocketHandler</button>
</div>
);
}
/*class App extends React.Component {
constructor(props) {
super(props);
this.state = {
welcomeString:""
}
}
buttonCliecked = () => {
console.log("clocked button");
this.setState({ welcomeString:"Welcome"})
}
onsockethandlerclicked = () => {
console.log("socket handler clicked");
socket.on('out', () => {
console.log("Recived message")
console.log(this.state.welcomeString);
});
}
render() {
return (
<div>
<header className="component-header">User Registration</header>
<label>{this.state.welcomeString}</label>
<button onClick={this.buttonCliecked}>setwelcomestring</button>
<button onClick={this.onsockethandlerclicked}>setSocketHandler</button>
</div>
);
}
}*/
export default App;

For those of us coming from a Redux background, useReducer can seem deceptively complex and unnecessary. Between useState and context, it’s easy to fall into the trap of thinking that a reducer adds unnecessary complexity for the majority of simpler use cases; however, it turns out useReducer can greatly simplify state management. Let’s look at an example.
As with my other posts, this code is from my booklist project. The use case is that a screen allows users to scan in books. The ISBNs are recorded, and then sent to a rate-limited service that looks up the book info. Since the lookup service is rate limited, there’s no way to guarantee your books will get looked up anytime soon, so a web socket is set up; as updates come in, messages are sent down the ws, and handled in the ui. The ws’s api is dirt simple: the data packet has a _messageType property on it, with the rest of the object serving as the payload. Obviously a more serious project would design something sturdier.
With component classes, the code to set up the ws was straightforward: in componentDidMount the ws subscription was created, and in componentWillUnmount it was torn down. With this in mind, it’s easy to fall into the trap of attempting the following with hooks
const BookEntryList = props => {
const [pending, setPending] = useState(0);
const [booksJustSaved, setBooksJustSaved] = useState([]);
useEffect(() => {
const ws = new WebSocket(webSocketAddress("/bookEntryWS"));
ws.onmessage = ({ data }) => {
let packet = JSON.parse(data);
if (packet._messageType == "initial") {
setPending(packet.pending);
} else if (packet._messageType == "bookAdded") {
setPending(pending - 1 || 0);
setBooksJustSaved([packet, ...booksJustSaved]);
} else if (packet._messageType == "pendingBookAdded") {
setPending(+pending + 1 || 0);
} else if (packet._messageType == "bookLookupFailed") {
setPending(pending - 1 || 0);
setBooksJustSaved([
{
_id: "" + new Date(),
title: `Failed lookup for ${packet.isbn}`,
success: false
},
...booksJustSaved
]);
}
};
return () => {
try {
ws.close();
} catch (e) {}
};
}, []);
//...
};
We put the ws creation in a useEffect call with an empty dependency list, which means it’ll never re-fire, and we return a function to do the teardown. When the component first mounts, our ws is set up, and when the component unmounts, it’s torn down, just like we would with a class component.
The problem
This code fails horribly. We’re accessing state inside the useEffect closure, but not including that state in the dependency list. For example, inside of useEffect the value of pending will absolutely always be zero. Sure, we might call setPending inside the ws.onmessage handler, which will cause that state to update, and the component to re-render, but when it re-renders our useEffect will not re-fire (again, because of the empty dependency list)—as a result that closure will go on closing over the now-stale value for pending.
To be clear, using the Hooks linting rule, discussed below, would have caught this easily. More fundamentally, it’s essential to break with old habits from the class component days. Do not approach these dependency lists from a componentDidMount / componentDidUpdate / componentWillUnmount frame of mind. Just because the class component version of this would have set up the web socket once, in componentDidMount, does not mean you can do a direct translation into a useEffect call with an empty dependency list.
Don’t overthink, and don’t be clever: any value from your render function’s scope that’s used in the effect callback needs to be added to your dependency list: this includes props, state, etc. That said—
The solution
While we could add every piece of needed state to our useEffect dependency list, this would cause the web socket to be torn down, and re-created on every update. This would hardly be efficient, and might actually cause problems if the ws sends down a packet of initial state on creation, that might already have been accounted for, and updated in our ui.
If we look closer, however, we might notice something interesting. Every operation we’re performing is always in terms of prior state. We’re always saying something like “increment the number of pending books,” “add this book to the list of completed,” etc. This is precisely where a reducer shines; in fact, sending commands that project prior state to a new state is the whole purpose of a reducer.
Moving this entire state management to a reducer would eliminate any references to local state within the useEffect callback; let’s see how.
function scanReducer(state, [type, payload]) {
switch (type) {
case "initial":
return { ...state, pending: payload.pending };
case "pendingBookAdded":
return { ...state, pending: state.pending + 1 };
case "bookAdded":
return {
...state,
pending: state.pending - 1,
booksSaved: [payload, ...state.booksSaved]
};
case "bookLookupFailed":
return {
...state,
pending: state.pending - 1,
booksSaved: [
{
_id: "" + new Date(),
title: `Failed lookup for ${payload.isbn}`,
success: false
},
...state.booksSaved
]
};
}
return state;
}
const initialState = { pending: 0, booksSaved: [] };
const BookEntryList = props => {
const [state, dispatch] = useReducer(scanReducer, initialState);
useEffect(() => {
const ws = new WebSocket(webSocketAddress("/bookEntryWS"));
ws.onmessage = ({ data }) => {
let packet = JSON.parse(data);
dispatch([packet._messageType, packet]);
};
return () => {
try {
ws.close();
} catch (e) {}
};
}, []);
//...
};
While slightly more lines, we no longer have multiple update functions, our useEffect body is much more simple and readable, and we no longer have to worry about stale state being trapped in a closure: all of our updates happen via dispatches against our single reducer. This also aids in testability, since our reducer is incredibly easy to test; it’s just a vanilla JavaScript function. As Sunil Pai from the React team puts it, using a reducer helps separate reads, from writes. Our useEffect body now only worries about dispatching actions, which produce new state; before it was concerned with both reading existing state, and also writing new state.
You may have noticed actions being sent to the reducer as an array, with the type in the zero slot, rather than as an object with a type key. Either are allowed with useReducer; this is just a trick Dan Abramov showed me to reduce the boilerplate a bit :)
What about functional setState()
Lastly, some of you may be wondering why, in the original code, I didn’t just do this
setPending(pending => pending - 1 || 0);
rather than
setPending(pending - 1 || 0);
This would have removed the closure problem, and worked fine for this particular use case; however, the minute updates to booksJustSaved needed access to the value of pending, or vice versa, this solution would have broken down, leaving us right where we started. Moreover, I find the reducer version to be a bit cleaner, with the state management nicely separated in its own reducer function.
All in all, I think useReducer() is incredibly under-utilized at present. It’s nowhere near as scary as you might think. Give it a try!
Happy coding!

React life cycle method for making API call when component is re-rendered

I have a component called <Header> where I have a log-in form that makes an API call to log a user in.
I have a function in my header component that makes some API calls to fetch some data and update the menu items in the header once successfully logged in:
componentDidMount() {
const { auth, actions, children } = this.props;;
if (auth.isLoggedIn) {
actions.getAssessmentRequest();
actions.getFirstSubsectionRequest();
}
}
The problem I am having is that the very first time the user logs in the above componentDidMount function does not trigger because the header component was already mounted the first time the page was loaded.
I have tried to use componentDidUpdate and componentWillReceiveProps but they get triggered multiple times and I get request timeout errors.
Any ideas which lifecycle method I could use to achieve this?

Yes you are on the right path, you should use the componentWillReceiveProps lifecycle method. The trick to prevent infinite loops and constantly making requests, you have to perform a check to test whether the props you care about actually changed or not:
componentDidMount() {
this.fetchData(this.props);
}
componentWillReceiveProps(nextProps) {
if(nextProps.auth.isLoggedIn !== this.props.auth.isLoggedIn) {
this.fetchData(nextProps);
}
}
fetchData(props) {
const { auth, actions, children } = props;
if (auth.isLoggedIn) {
actions.getAssessmentRequest();
actions.getFirstSubsectionRequest();
}
}

I can't tell you why it is called multiple times, but I can tell you that it should not matter. The problem is that you're not comparing the props for what has changed. If you do this, the code will behave the way you want:
componentWillReceiveProps(newProps) {
const { auth, actions, children } = newProps;
if (auth.isLoggedIn !== this.props.auth.isLogin) {
actions.getAssessmentRequest();
actions.getFirstSubsectionRequest();
}
}
See also the official ReactJS documentation, which states: https://facebook.github.io/react/docs/react-component.html#componentwillreceiveprops
Hope this helps.

Redux mapDispatchToProps not getting proper payload

So there is this simplified structure in my app:
In component i have :
handlePageClick(data) {
this.props.onChangePage(data.selected + 1);
this.props.onSearchSomething(this.props.PM);
}
In my Container :
const mapDispatchToProps = dispatch => ({
onUpdateForm: (propPath, val) => {
dispatch(updatePMForm(propPath, val));
},
onSearchSomething: (payload) => {
// TODO: process the PM state here when integrating with the server in order to extract
// the proper payload out of the state object
dispatch(searchSomething(15, payload));
},
onChangePage: (pageNumber) => {
dispatch(changePage(pageNumber));
},
});
So when i trigger pageClick, and onChangePage returns newState, in mapDispatchToProps dispatch(searchSomething(15, payload)) receive previous State in payload, that hasn't been updated yet.

You should use componentDidUpdate or componentWillUpdate and diff previous state with current one and then call this.props.onSearchSomething with updated value from the store rather than call it one after another in handlePageClick. Why is that? State changes in a component are potentially asynchronous and almost in all cases there's no way that the component's props will be updated between this.props.onChangePage and this.props.onSearchSomething calls. Please read this issue for better understanding what I'm talking about.
But to help you out a bit some time ago I created a small utility map-props-changes-to-callbacks to assign callbacks in your components to specific changes in redux store. Perhaps that can be helpful in your case and you can write your code like that:
handlePageClick(data) {
this.props.onChangePage(data.selected + 1)
}
onPageChanged() {
this.props.onSearchSomething(this.props.PM)
}
Also, you should consider moving your logic to a single action so you can just dispatch one action and get the search result in return.

Why componentWillMount is called after rendering?

I am working with React and I am trying to understand the lifecycle. I am doing a componentWillMount method in order to get the props I need before the render occurs. I need to know how to update the state when the view loads.
All I am trying to do is a GET request in order to get a list of dealers for a Casino Game. Basically, I am missing 1 or 2 steps which are for render the dealers's list in the DOM
I will show what I am doing with my code and after that I will explain what I want
Actions part
getDealerActions.js
class GetDealersActions {
constructor () {
this.generateActions('dealerDataSuccess', 'dealerDataFail');
}
getDealers (data) {
const that = this;
that.dispatch();
axios.get('someroute/get-dealers/get-dealers')
.then(function success (response) {
that.actions.dealerDataSuccess({...response.data});
})
}
};
then we move to the stores
getDealersStore.js
class GetDealersStore {
constructor () {
this.state = {
dealerData : null,
};
}
#bind(GetDealersActions.dealerDataSuccess)
dealerDataSuccess (data) {
this.setState({
dealerData : data,
});
console.log(this.state.dealerData);
}
}
in this case that console.log(this.state.dealerData); returns something like this which is exactly what I need
Object {dealersData: Array[3]}
the problems comes in the component part, honestly because I don't know how to handle the data here
#connectToStores
export default class Dealers extends Component {
static contextTypes = {
router : React.PropTypes.func,
}
constructor (props) {
super(props);
this.state = {}
}
static getStores () {
return [ GetDealersStore ];
}
static getPropsFromStores () {
return GetDealersStore.getState();
}
componentWillMount () {
console.log('###', this.props);
GetDealersActions.getDealers();
}
render () {
console.log('>>>', this.props);
let content;
if (this.state.dealerData) {
content = this.state.dealerData.map((item) => {
return <div key={item.CardId}>{item}</div>;
});
} else {
content = <div>Loading . . .</div>;
}
return (
<div>
<div>{content}</div>
</div>
);
}
}
all I get here <div>{content}</div> is Loading . . . because this.state is coming like this Object {}
A weird situation I am getting here, is that this view is rendering twice, the 1st time is rendering, and the console.log('>>>', this.props); returns this >>> Object {params: Object, query: Object} and the second time it renders, fires this >>> Object {params: Object, query: Object, dealerData: Object} which is what I need.
So, why componentWillMount is waiting the render method in order to get fired ?

It's not weird at all. componentWillMount will fire before render, and in the first-pass you are invoking an action to get the dealers GetDealersActions.getDealers(); which is basically an async command. Since it is async, the component will render once before it gets data, and then again after the store publishes a changed event, which will re-trigger rendering.
Here is an approximation of the sequence of actions happening in your example:
componentWillMount invokes getDealers command (which is async)
initial render with default component state
Async operation completed in action creator and store is set with dealer data
store publishes a changed event, which re-triggers rendering
second render invoked with the dealer data in component state.
The problem is that React will run it's lifecycle methods in a certain sequence, not caring about you invoking some async method. So basically you don't have a way to stop rendering just because you invoked a command to get the dealers. That is a limitation of react (or a feature), which surfaces when combined with async programming and you should accept it as is.
If you accept the fact that React will render twice, you can utilize that in your favor, so on first render you could just show a loading indicator (e.g. a spinning wheel) and when the data loads you just display it in the second render.
However, if you are not convinced and still want to avoid double-rendering in the initial load, you could do prefetching of the data before you mount the application component, which would ensure that initial data is loaded in the store before the first render, which would mean that you wouldn't have to invoke getDealers in componentWillMount since the data would already be in the store on the first render.
As a reminder, double-rendering is not a significant performance problem, like it would be in Angular.js or Ember.js, since React is very efficient at DOM manipulation, but it could produce some UX issues if not handled properly.