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How to fetch API as soon as page is loaded in React?

Whenever I visit a page it should automatically fetch the API
import React from 'react'
const Component = () => {
fetch("api url").then((res) => console.log(res))
return (
<div>comp</div>
)
}
export default Component

It is very simple using react hook use effect please learn basics of useffect hook on react docs or any youtube tutorial and as for the answer
import React, { useEffect } from 'react'
const comp = () => {
useEffect(() => {
fetch("api url").then((res)=>console.log(res))
}, [])
return (
<div>comp</div>
)
}
export default comp
here empty dependency means every time page loads only once

use the useEffect for this.
The useEffect method will execute the passed callback on the mount of the component and on every time one of the dependency array parameters is changed. therefore:
const Comp = () => {
useEffect(() => {
fetch("api url").then((res)=>console.log(res))
}, []);
return (
<div>comp</div>
)
}
Will make the callback to fire only once (because the empty dependency array) on the component mount.

You should use the useEffect Hook in your principal component like app.js
import React, {useEffect} from 'react'
useEffect(() => {
fetch("api url").then((res)=>console.log(res))
}, []);
Be careful, this manipulation can consume a lot of resources (a lot of data to fetch etc.)
Thery

import React, { useState, useEffect } from 'react'
const Comp = () => {
const [ data, setData ] = useState([]);
const getData = async () => {
const res = await fetch("api url");
const data = await res.json();
setData(data)
}
useEffect(()=>{ getData() },[]);
return (
<>
<div>comp</div>
// dispaly your data here from data state
</>
)
}
export default Comp;

Fetch and use data with useState
const initialValue = {};
const comp = () => {
const [data, setData] = useState(initialValue);
useEffect(() => {
let ignore = false;
const fetchData = async () => {
const res = fetch("api url");
if (ignore) { return; }
setData(res.json())
return () => {
ignore = true;
}
}
, [])
return (
<div>comp {data.prop}</div>
)
}
More on working with state
More about useEffect life cycle
Hope it helps

You don't need to use the API function like this, it will be called continuously, you need to use useEffect hook, when your component reloads useEffect will be called, and you can learn about the useEffect dependency here,
import React, { useEffect, useState } from 'react'
const comp = () => {
const [data, setData] = useState([]);
useEffect(() => {
fetch("api url").then((res)=> {
console.log(res)
setData(res)
} )
}, [])
return (
// use data state to show the data here
<div>comp</div>
)
}
export default comp;

Nested Query fetch Data

categories name
pic of datas
import {useState, useEffect,useMemo} from 'react';
import { gql, useQuery } from '#apollo/client';
import {GET_CLOTHES} from "./GetClothes.js"
import ArrowForwardIosIcon from '#mui/icons-material/ArrowForwardIos';
import ArrowBackIosNewIcon from '#mui/icons-material/ArrowBackIosNew';
function Clothes() {
const { loading, error, data } = useQuery(GET_CLOTHES);
const [products,setProducts] = useState([]);
const [index,setIndex] = useState(0);
useEffect(() => {
if (data) {
setProducts(data.categories.products);
console.dir(data.categories.products);
}
},[data]);
//console.dir(products);
/*
useEffect(() => {
if(!loading && data){
setProducts(data);
}
}, [loading, data])
*/
if (loading) return 'Loading...'
if (error) return `Error! ${error.message}`
return <div>
{
// Products is actually products
products?.map((product,index) => {
if (product.name === 'clothes') { //filter
// Iterate through products.products to obtain the product data.
const {name,brand,description,gallery,category} = product;
return <p>{name}</p>
}})
}
</div>
}
export default Clothes;
`
Hello everyone, I am trying to fetch my datas from graphlq however I can fetch to first data from array but when I try reach one of the nested array I got undefined.
How I can solve this issue.

You don't need to keep data as a state variable
data will be undefined until loading is false. The first pass through your console.log it will be undefined.
A typical pattern might be:
function Clothes() {
const { loading, error, data } = useQuery(GET_CLOTHES);
if (data) {
… render the data
} else if (error) {
…handle the error
return <Error /> // return an error component
} else return <Loading /> // return a spinner or other progress indicator
}
Note that your function must return a jsx component - it cannot return a string.

Ok. First of all, categories is an array, so products isn't defined as a property in the array. Its items do have the products property.
Second of all, products is a derived state. You do not need make a separate it as its own useState
import {useState, useEffect,useMemo} from 'react';
import { gql, useQuery } from '#apollo/client';
import {GET_CLOTHES} from "./GetClothes.js"
import ArrowForwardIosIcon from '#mui/icons-material/ArrowForwardIos';
import ArrowBackIosNewIcon from '#mui/icons-material/ArrowBackIosNew';
function Clothes() {
const { loading, error, data } = useQuery(GET_CLOTHES);
const [index,setIndex] = useState(0);
if (loading) return 'Loading...'
if (error) return `Error! ${error.message}`
return <div>
{
data.categories.flatMap(x => x.products).map(product => {
if (product.name === 'clothes') { //filter
// Iterate through products.products to obtain the product data.
const {name,brand,description,gallery,category} = product;
return <p>{name}</p>
} else {
return null;
}
})
}
</div>
}
export default Clothes;

I lost props after reloading the page in react

I used axios in useEffect of my wrapper component and I sent the data as props to the other component "singleQuestionnaire", in singleQuestionnaire component, I destructured the data, in the first try, it works fine, but after reloading the page it doesn't work with an error : can not read property "map" of undefined
import React, { useEffect, useState } from "react";
import SingleQuestionnaire from "./SingleQuestionnaire";
import { fetchQuestions } from "../../../api/index";
const Questionnaires = ({ match }) => {
const [questions, setQuestions] = useState([]);
const pid = match.params.id;
const getQuestionnaire = async (pid) => {
try {
const { data } = await fetchQuestions(pid);
console.log(data.data, "action in component");
setQuestions(data.data);
} catch (error) {
console.log(error);
}
};
useEffect(() => {
getQuestionnaire(pid);
}, []);
console.log("all questions", questions);
return (
<div>
<SingleQuestionnaire questions={questions} setQuestions={setQuestions} />
</div>
);
};
export default Questionnaires;
and this is my singleQuestionnaire component:
import React, { useEffect, useState } from "react";
const SingleQuestionnaire = ({ questions, setQuestions }) => {
const [questionnaire, setQuestionnaire] = useState([]);
console.log(questions);
const { data } = questions;
console.log("data", data.farmInformationQuestionnaireData);
return <div>simple component</div>;
};
export default SingleQuestionnaire;
For the first time, in console I can see the data "data.data.farmInformationQuestionnaireData". It's an array but for the second time it's undefind.

because questions in SingleQuestionnaire is an empty array before we fetch
which causes an error here
const { data } = questions;
you can add a loading text because initially questions will be an empty array then it will be your res.data (assuming it's an object)
const SingleQuestionnaire = ({ questions, setQuestions }) => {
const [questionnaire, setQuestionnaire] = useState([]);
console.log(questions);
if(questions.length === 0 ) return <h1> Loading</h1>
const { data } = questions;
console.log("data", data.farmInformationQuestionnaireData);
return <div>simple component</div>;
};

it is happening because of the async API call. When you make an async call, the thread does not wait, it moves on and it starts executing other things.
Now your async call might be complete but your callback will not be executed until the stack is empty, that's just how javaScript works. I recommend you use some kind of loader gif or text
{questions ? <SingleQuestionnaire questions={questions} setQuestions={setQuestions} /> : <p>Loading...</p>}

React Hooks/Context & Elastictic UI. Problem with fetched data (REST) in function Component

I'm quite new to React Hooks/Context so I'd appreciate some help. Please don' t jump on me with your sharp teeth. I Checked other solutions and some ways i've done this before but can't seem to get it here with the 'pick from the list' way.
SUMMARY
I need to get the municipios list of names inside of my const 'allMunicipios'(array of objects) inside of my Search.js and then display a card with some data from the chosen municipio.
TASK
Get the data from eltiempo-net REST API.
Use Combobox async element from Elastic UI to choose from list of municipios.
Display Card (from elastic UI too) with some info of chosen municipio.
It has to be done with function components / hooks. No classes.
I'd please appreciate any help.
WHAT I'VE DONE
I've created my reducer, context and types files in a context folder to fecth all data with those and then access data from the component.
I've created my Search.js file. Then imported Search.js in App.js.
I've accesed the REST API and now have it in my Search.js
PROBLEM
Somehow I'm not beeing able to iterate through the data i got.
Basically i need to push the municipios.NOMBRE from api to the array const allMunicipios in my search.js component. But when i console log it it gives me undefined. Can;t figure out why.
I'll share down here the relevant code/components. Thanks a lot for whoever takes the time.
municipiosReducer.js
import {
SEARCH_MUNICIPIOS,
CLEAR_MUNICIPIOS,
GET_MUNICIPIO,
GET_WEATHER,
} from "./types";
export default (state, action) => {
switch (action.type) {
case SEARCH_MUNICIPIOS:
return {
...state,
municipios: action.payload,
};
case GET_MUNICIPIO:
return {
...state,
municipio: action.payload,
};
case CLEAR_MUNICIPIOS:
return {
...state,
municipios: [],
};
case GET_WEATHER: {
return {
...state,
weather: action.payload,
};
}
default:
return state;
}
};
municipiosContext.js
import { createContext } from "react";
const municipiosContext = createContext();
export default municipiosContext;
MunicipiosState.js
import React, { createContext, useReducer, Component } from "react";
import axios from "axios";
import MunicipiosContext from "./municipiosContext";
import MunicipiosReducer from "./municipiosReducer";
import {
SEARCH_MUNICIPIOS,
CLEAR_MUNICIPIOS,
GET_MUNICIPIO,
GET_WEATHER,
} from "./types";
const MunicipiosState = (props) => {
const initialState = {
municipios: [],
municipio: {},
};
const [state, dispatch] = useReducer(MunicipiosReducer, initialState);
//Search municipios
//In arrow functions 'async' goes before the parameter.
const searchMunicipios = async () => {
const res = await axios.get(
`https://www.el-tiempo.net/api/json/v2/provincias/08/municipios`
// 08 means barcelona province. This should give me the list of all its municipios
);
dispatch({
type: SEARCH_MUNICIPIOS,
payload: res.data.municipios,
});
};
//Get Municipio
const getMunicipio = async (municipio) => {
const res = await axios.get(
`https://www.el-tiempo.net/api/json/v2/provincias/08/municipios/${municipio.CODIGOINE}`
//CODIGOINE is in this REST API kind of the ID for each municipio.
//I intent to use this later to get the weather conditions from each municipio.
);
dispatch({ type: GET_MUNICIPIO, payload: res.municipio });
};
const dataMunicipiosArray = [searchMunicipios];
//Clear Municipios
const clearMunicipios = () => {
dispatch({ type: CLEAR_MUNICIPIOS });
};
return (
<MunicipiosContext.Provider
value={{
municipios: state.municipios,
municipio: state.municipio,
searchMunicipios,
getMunicipio,
clearMunicipios,
dataMunicipiosArray,
}}
>
{props.children}
</MunicipiosContext.Provider>
);
};
export default MunicipiosState;
Search.js
import "#elastic/eui/dist/eui_theme_light.css";
import "#babel/polyfill";
import MunicipiosContext from "../contexts/municipiosContext";
import MunicipiosState from "../contexts/MunicipiosState";
import { EuiComboBox, EuiText } from "#elastic/eui";
import React, { useState, useEffect, useCallback, useContext } from "react";
const Search = () => {
const municipiosContext = useContext(MunicipiosContext);
const { searchMunicipios, municipios } = MunicipiosState;
useEffect(() => {
return municipiosContext.searchMunicipios();
}, []);
const municipiosFromContext = municipiosContext.municipios;
const bringOneMunicipio = municipiosContext.municipios[0];
let municipiosNames = municipiosFromContext.map((municipio) => {
return { label: `${municipio.NOMBRE}` };
});
console.log(`municipiosFromContext`, municipiosFromContext);
console.log(`const bringOneMunicipio:`, bringOneMunicipio);
console.log(`municipiosNames:`, municipiosNames);
const allMunicipios = [
{ label: "santcugat" },
{ label: "BARCELONETA" },
{ label: "BARCE" },
];
const [selectedOptions, setSelected] = useState([]);
const [isLoading, setLoading] = useState(false);
const [options, setOptions] = useState([]);
let searchTimeout;
const onChange = (selectedOptions) => {
setSelected(selectedOptions);
};
// combo-box
const onSearchChange = useCallback((searchValue) => {
setLoading(true);
setOptions([]);
clearTimeout(searchTimeout);
// eslint-disable-next-line react-hooks/exhaustive-deps
searchTimeout = setTimeout(() => {
// Simulate a remotely-executed search.
setLoading(false);
setOptions(
municipiosNames.filter((option) =>
option.label.toLowerCase().includes(searchValue.toLowerCase())
)
);
}, 1200);
}, []);
useEffect(() => {
// Simulate initial load.
onSearchChange("");
}, [onSearchChange]);
return (
<div>
<EuiComboBox
placeholder="Search asynchronously"
async
options={options}
selectedOptions={selectedOptions}
isLoading={isLoading}
onChange={onChange}
onSearchChange={onSearchChange}
/>
<button>Lista de municipios</button>
</div>
);
};
export default Search;
also the
Home.js
import React, { useState } from "react";
import { EuiComboBox, EuiText } from "#elastic/eui";
// import { DisplayToggles } from "../form_controls/display_toggles";
import "#babel/polyfill";
import "#elastic/eui/dist/eui_theme_light.css";
import Search from "./Search";
import MunicipioCard from "./MunicipioCard";
const Home = () => {
return (
<div>
<EuiText grow={false}>
<h1>Clima en la provincia de Barcelona</h1>
<h2>Por favor seleccione un municipio</h2>
</EuiText>
<Search />
<MunicipioCard />
</div>
);
};
export default Home;
App.js
import "#babel/polyfill";
import "#elastic/eui/dist/eui_theme_light.css";
import { EuiText } from "#elastic/eui";
import React from "react";
import Home from "./components/Home";
import MunicipiosState from "./contexts/MunicipiosState";
import "./App.css";
function App() {
return (
<MunicipiosState>
<div className="App">
<EuiText>
<h1>App Component h1</h1>
</EuiText>
<Home />
</div>
</MunicipiosState>
);
}
export default App;

You are using forEach and assigning the returned value to a variable, however forEach doesn't return anything. You should instead use map
let municipiosNames = municipiosFromContext.map((municipio) => {
return `label: ${municipio.NOMBRE}`;
});
As per your comment:
you data is loaded asynchronously, so it won't be available on first render and since functional components depend on closures, you onSearchChange function takes the value from the closure at the time of creation and even if you have a setTimeout within it the updated value won't reflect
The solution here is to add municipiosFromContext as a dependency to useEffect
const onSearchChange = useCallback((searchValue) => {
setLoading(true);
setOptions([]);
clearTimeout(searchTimeout);
// eslint-disable-next-line react-hooks/exhaustive-deps
searchTimeout = setTimeout(() => {
// Simulate a remotely-executed search.
setLoading(false);
setOptions(
municipiosNames.filter((option) =>
option.label.toLowerCase().includes(searchValue.toLowerCase())
)
);
}, 1200);
}, [municipiosFromContext]);
useEffect(() => {
// Simulate initial load.
onSearchChange("");
}, [onSearchChange]);

How to iterate through data and display them in JSX in ReactJS?

I have a function that makes a call to the server and retrieves data in a form of array of json objects, what i want is to iterate through the data and display them in the JSX .
Thw Problem is
No thing is being displayed on the screen, not even getting an error. and when I console.log the response i got this:
below is the component
import React from 'react';
import axios from 'axios';
function Supplier(){
let suppliers_list=[];
React.useEffect(() => {
getAllSuppliers();
});
const getAllSuppliers = () =>{
return axios.get('http://localhost:4000/supplier',supplierData).then(
response=>{
let allSuppliers = response.data;
allSuppliers.forEach(element => {
suppliers_list.push(
<li>{element.supplier_name}</li>
);
});
},error =>{
//handle error
}
);
}
return(
<div>
<ul>
{suppliers_list}
</ul>
</div>
)
}
export default Supplier;
and when I console.log the suppliers_list I got this:

Change your code like below,
import React from 'react';
import axios from 'axios';
function Supplier(){
const [suppliersList, setSuppliersList] = React.useState([]);
React.useEffect(() => {
getAllSuppliers();
}, []); // Hoping you want to execute getAllSuppliers function only once, so [] empty square braces
const getAllSuppliers = () =>{
return axios.get('http://localhost:4000/supplier', supplierData).then(
response=>{
setSuppliersList(response.data);
},error =>{
//handle error
}
);
}
return(
<div>
<ul>
{suppliersList.map(supplierObject => {
return <li>{supplierObject.supplier_name}</li>
})}
</ul>
</div>
)
}
export default Supplier;