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Router.push is returning my objects as undefined, the array length is correct but the value is "" in Next.js [duplicate]

I got a problem with my dynamic route. It look like this
[lang]/abc
I am trying to get query value from [lang] but when I using useRouter/withRouter i got query during 2-3 render of page ( on first i got query.lang = undefined ). its possible to get in 1 render or use any technique ?

I found something:
isReady: boolean - Whether the router fields are updated client-side and ready for use. Should only be used inside of useEffect methods and not for conditionally rendering on the server.
https://nextjs.org/docs/api-reference/next/router#router-object
And the code would be like:
const router = useRouter();
useEffect(()=>{
if(!router.isReady) return;
// codes using router.query
}, [router.isReady]);

It's impossible to get the query value during the initial render.
Statically optimized pages are hydrated without the route parameters, so the query is an empty object ({}).
Next.js will populate the query after the page has been hydrated.
Next.js 10.0.5 and up
To determine if the route params are ready, you can use router.isReady inside a useEffect hook. For an example, see the answer provided by #doxylee.
Before Next.js 10.0.5
At first render of a dynamic route router.asPath and router.route are equal. Once query object is available, router.asPath reflects it.
You can rely on the query value within a useEffect hook after asPath has been changed.
const router = useRouter();
useEffect(() => {
if (router.asPath !== router.route) {
// router.query.lang is defined
}
}, [router])
GitHub Issue - Add a "ready" to Router returned by "useRouter"

In NextJS 9+, one way to ensure route parameters are immediately available for page components is to get them from the context arg passed to getServerSideProps() and pass to the component as props.
For a page like [id].js,
export function getServerSideProps(context) {
return {
props: {params: context.params}
};
}
export default ({params}) => {
const {id} = params;
return <div>You opened page with {id}</div>;
};

This is a great question and one that took a few days for me to figure out what the best approach is.
I have personally found three viable solutions to the problem of validating dynamic route path params or even just route path params in general.
The three solutions are
SSR (don't recommend) [Next >= 10]
useRouter
Middleware [Next 12 required]
In my examples a will use a route that requires a reset-token or it should be redirected.
SSR
Firstly server side rending with getServerSideProps.
Vercel recommends to use SSR as a last resort and I would highly recommend not using SSR when able (time to byte & cost).
We suggest trying Incremental Static Generation or Client-side Fetching and see if they fit your needs.
https://vercel.com/blog/nextjs-server-side-rendering-vs-static-generation
But in the case that you do, say there is some server side api validation call you require to validate the query param.
export const getServerSideProps = async (context) => {
const { token } = context.query;
if (!token) {
return {
redirect: {
permanent: false,
destination: "/",
}
}
}
return {
props: {}
// props: { token }
// You could do this either with useRouter or passing props
}
}
useRouter Secondly the easiest useRouter. When I first did this I came across the problem when nextjs/react hydrates there will be a point when the query params are null. Luckily useRouter has isReady!
import Router, { useRouter } from "next/router";
const { query, isReady } = useRouter();
useEffect(() => {
if (!isReady) return;
if (!query.token) {
Router.push("/")
}
}, [isReady])
Middleware now this is my personal favourite as it seperates the functionality in a clean way imo.
I found this based of a vercel example. I would highly recommend reading through a bunch of these to find best practices.
https://github.com/vercel/examples/
import { NextResponse, NextRequest } from 'next/server'
export async function middleware(req) {
const { pathname, searchParams } = req.nextUrl
if (pathname == '/reset-token') {
const index = searchParams.findIndex(x => x.key === "token")
// You could also add token validation here.
if (!index) {
return NextResponse.redirect('/')
}
}
return NextResponse.next()
}
Here is the repo which has some cool filtering of query parameters.
This is a more soft approach instead of hard redirecting.
https://github.com/vercel/examples/tree/main/edge-functions/query-params-filter
Nico also has a great answer on this, expect I wouldn't recommend using hooks like in his example, instead use isReady.
https://stackoverflow.com/a/58182678/4918639

For Class Component Lovers
The even better approach is to listen for a dedicated event for this routeChangeComplete using this.props.router.events.on method, inside componentDidMount if you're using class component -
routeChangeComplete = () => {
// this WILL have valid query data not empty {}
console.log(this.props.router.query);
};
componentDidMount() {
this.props.router.events.on("routeChangeComplete", this.routeChangeComplete);
}
componentWillUnmount() {
this.props.router.events.off("routeChangeComplete", this.routeChangeComplete);
}
Ref: https://nextjs.org/docs/api-reference/next/router#routerevents
routeChangeComplete: Fires when a route changed completely.
Practically when isReady has become true or when router.query object has data.

For NextJS version - 12.0.8
"If you export a function called getServerSideProps (Server-Side Rendering) from a page, Next.js will pre-render this page on each request using the data returned by getServerSideProps."
=async functions
refference:https://nextjs.org/docs/basic-features/data-fetching/get-server-side-props#getserversideprops
Simply putting that async function on the page notifies NextJS of its presence.During prerendering stage of the component, the query object of the router will be empty.
isReady: boolean - Whether the router fields are updated client-side and ready for use. Should only be used inside of useEffect methods and not for conditionally rendering on the server.
refference: https://nextjs.org/docs/api-reference/next/router
solution:
import { useRouter } from 'next/router';
const Fn = () =>{
const router = useRouter();
const { param } = router.query;
const fetchData = async () => {
await fetch();
}
useEffect(() => {
fetchCat();
}, [router.isReady]);
}

I resolved my problem that I need it in Hoc component.
I wrapped using withRouter(withLocale(Comp)) and create conditional in HOC
export default function withLocale(WrappedPage) {
const WithLocale = ({ router, ...props }) => {
const { lang } = router.query;
if (!lang || !isLocale(lang)) {
return <Error statusCode={404} />;
}
return (
<LocaleProvider lang={lang}>
<WrappedPage {...props} />
</LocaleProvider>
);
};
return WithLocale;
}

Next.js <= 10.0.5
This is a good work around, I found around from this comment
Add useQuery.ts helper file
// useQuery.js
import { useRouter } from 'next/router';
// Resolves query or returns null
export default function useQuery() {
const router = useRouter();
const ready = router.asPath !== router.route;
if (!ready) return null;
return router.query;
}
usage
// In your components (instead of useRouter)
const query = useQuery();
useEffect(() => {
if (!query) {
return;
}
console.log('my query exists!!', query);
}, [query]);

Class Component | 12/16/2022 | React JS 18.2.0 | Next JS 13.0.6
I got the answer for those who want to use Class Component. This was actually nowhere to be found ! Enjoy !
You will add if(this.props.router.isReady) and include return in the condition in render().
.
.
import { withRouter } from 'next/router';
import { Component } from 'react';
class User extends Component {
...
render() {
if(this.props.router.isReady){ // Add this condition and include return ()
// Do anything
console.log(this.props.router.query) // Log 'query' on first render
return (
<div>
<SearchBar pid={this.props.router.query.pid} /> // Pass the query params to another component if needed
</div>
);
}
}
}
export default withRouter(User);

react code splitting: is the argument for the import() function not a string

This is very bizarre. During my attempt at code-splitting, I encountered this:
const g = "bi";
const importStr = `react-icons/${g.toLowerCase()}`;
console.log(importStr);
console.log(importStr === `react-icons/bi`);
import(importStr).then(module => {
console.log(module);
});
import(`react-icons/bi`).then(module => {
console.log(module);
});
In the above code, if I import "importStr", then the import throws an error:
Uncaught (in promise) Error: Cannot find module 'react-icons/bi'
But if I directly import "react-icons/bi", then there is no issue. As you see,
importStr === `react-icons/bi`
Why and how do I fix this? I can't actually directly use "react-icons/bi" because g is dynamic and could take other values.

I quote from the following comment
Webpack performs a static analyse at build time. It doesn't try to infer variables which that import(test) could be anything, hence the failure. It is also the case for import(path+"a.js").
Because of the tree shaking feature webpack tries to remove all unused code from the bundle. That also means something similar could work
import("react-icons/" + g)
Edit: as per your suggestion I updating this to
import("react-icons/" + g.toLowerCase()+ '/index.js')

An easy way to implement code splitting in React is with lazy loading, as seen here (this might be easier than importing a dynamic string):
const OtherComponent = React.lazy(() => import('./OtherComponent'));
This implementation will load the bundle with OtherComponent only when it is first rendered.
Example from reactjs.org:
import React, { Suspense } from 'react';
const OtherComponent = React.lazy(() => import('./OtherComponent'));
const AnotherComponent = React.lazy(() => import('./AnotherComponent'));
function MyComponent() {
return (
<div>
<Suspense fallback={<div>Loading...</div>}>
<section>
<OtherComponent />
<AnotherComponent />
</section>
</Suspense>
</div>
);
}
More info on React.lazy

How to add Nextjs cookie based secure authentication?

I have a small issue. I'm very very very new to Nextjs and I'm trying to learn by making a app. I have managed to make a Login system using next and I have few issues when securing routes. I have successfully added a cookie after successful login. Now I want to validate the cookie whenever user go to a protected route. I have followed below steps using this tutorial.
Made a Higher order component and checked the cookie validation using it.
Wrap the protected component using it.
Below is my HOD.
import { useRouter } from "next/router";
import Cookies from 'js-cookie';
const withAuth = (WrappedComponent) => {
return (props) => {
if (typeof window !== "undefined") {
const Router = useRouter();
const accessToken = Cookies.get('token');
if (!accessToken) {
Router.replace("/");
return null;
}
return <WrappedComponent {...props} />;
}
return null;
};
};
export default withAuth;
And then I have wrapped my component using above HOD.
import React, { Component } from 'react';
import withAuth from '../utils/withAuth';
class Home extends Component {
render() {
return (
<div>
HOME
</div>
);
}
}
export default withAuth(Home);
ISSUE #1
Above HOD is showing a console warning saying below.
Warning: Expected server HTML to contain a matching in .
div
Is their anyway I can fix this issue? As per some github answer I have found this can be solved using useEffect. SOURCE
Can anyone help me with this?
ISSUE #2
In this way, I have to wrap each and every protected component with my HOD. Is this the correct way of doing this or is there any other way to do this better than this?
Thank you so much or your support.

After spending some time. I was able to fix the issue by using below code. Now I just want to know the answer for 2nd issue mentioned above.
ISSUE #2 In this way, I have to wrap each and every protected component with my HOD. Is this the correct way of doing this or is there any other way to do this better than this?
Thank you so much or your support.
Code I use to fix the issue
import Router from 'next/router'
import Cookies from 'js-cookie';
import React, { useState, useEffect } from 'react';
const withAuth = (WrappedComponent) => {
return (props) => {
const [isLoggedIn, setLoginStatus] = useState(false);
useEffect(() => {
if (typeof window !== "undefined") {
const accessToken = Cookies.get('token');
if (accessToken) {
setLoginStatus(true)
}
else {
Router.push("/")
}
}
}, []);
if (isLoggedIn) {
return <WrappedComponent {...props} />;
} else {
return null;
}
}
};
export default withAuth;

Data from Gatsby GraphQL always returns undefined?

Gatsby noob here so please bear with me. I have a component that accepts props from the index.js where it is supposed to receive data from an array of objects but will always receive the error TypeError: Cannot read property 'map' of undefined where it's referring to the Hero.js component index.js is calling for.
My assumption is that the data being queried in index.js is either not specific enough or that it is rendering the component before data is received. Here is the index.js file:
import { graphql } from 'gatsby';
import { Layout, SEO, Hero } from 'components';
const IndexPage = ({ data }) => {
const dataFetch = data.contentfulTemplateIndex.heroes;
let tester = () => {
for (let count = 0; count < dataFetch.length; count++) {
return <Hero {...props} />;
}
};
console.log(dataFetch);
let props = {
impactText: dataFetch.impactText,
labels: dataFetch.labels,
primaryLabel: dataFetch.primaryLabel,
location: dataFetch.location
// supportingText: dataFetch.supportingText.json
};
return (
<Layout>
{dataFetch && tester()}
</Layout>
);
};
export const query = graphql`
query {
contentfulTemplateIndex {
heroes {
image {
fluid {
src
}
}
impactText
labels
location
primaryLabel
supportingText {
json
}
}
}
}
`;
export default IndexPage;
Here is the Hero.js component which index.js is calling:
import { Link } from 'gatsby';
import { documentToReactComponents } from '#contentful/rich-text-react-renderer';
import cx from 'classnames';
import styles from './hero.module.scss';
const Hero = (props) => {
return (
<div>
<ul>
<Link className={styles.pills}>{props.primaryLabel}</Link>
{props.labels.map((label) => {
return <Link className={styles.pills}>{label}</Link>;
})}
</ul>
<div className={styles.grid}>
<h1>{props.impactText}</h1>
</div>
</div>
);
};
export default Hero;

It's impossible for an outsider to debug your code without a minimum reproducable example.
The best way to debug GraphQL is to use the GraphiQL interface of your browser.
Run gatsby develop. If it fails because of the TypeError remove the lines of code that cause the type error (but not the code of your GraphQL query!). You need to get your development server runnning.
Open your browser, use the URL: http://localhost:8000/___graphql
Copy your graphQL query from your code and paste it into the GraphiQL query window.
Can you access your data there? If not you made a mistake writing your query or the data is not where it's supposed to be.
This way you can make sure the data exists.
It also helps to console.log(props) so you can examine the data object:
const Hero = (props) => {
console.log(props);
return (

Why can't I curry a react component?

I've been getting started with react-redux and finding it a very interesting way to simplify the front end code for an application using many objects that it acquires from a back end service where the objects need to be updated on the front end in approximately real time.
Using a container class largely automates the watching (which updates the objects in the store when they change). Here's an example:
const MethodListContainer = React.createClass({
render(){
return <MethodList {...this.props} />},
componentDidMount(){
this.fetchAndWatch('/list/method')},
componentWillUnmount(){
if (isFunction(this._unwatch)) this._unwatch()},
fetchAndWatch(oId){
this.props.fetchObject(oId).then((obj) => {
this._unwatch = this.props.watchObject(oId);
return obj})}});
In trying to supply the rest of the application with as simple and clear separation as possible, I tried to supply an alternative 'connect' which would automatically supply an appropriate container thus:
const connect = (mapStateToProps, watchObjectId) => (component) => {
const ContainerComponent = React.createClass({
render(){
return <component {...this.props} />
},
componentDidMount(){
this.fetchAndWatch()},
componentWillUnmount(){
if (isFunction(this._unwatch)) this._unwatch()},
fetchAndWatch(){
this.props.fetchObject(watchObjectId).then((obj) => {
this._unwatch = this.props.watchObject(watchObjectId);
return obj})}
});
return reduxConnect(mapStateToProps, actions)(ContainerComponent)
};
This is then used thus:
module.exports = connect(mapStateToProps, '/list/method')(MethodList)
However, component does not get rendered. The container is rendered except that the component does not get instantiated or rendered. The component renders (and updates) as expected if I don't pass it as a parameter and reference it directly instead.
No errors or warnings are generated.
What am I doing wrong?

This is my workaround rather than an explanation for the error:
In connect_obj.js:
"use strict";
import React from 'react';
import {connect} from 'react-redux';
import {actions} from 'redux/main';
import {gets} from 'redux/main';
import {isFunction, omit} from 'lodash';
/*
A connected wrapper that expects an oId property for an object it can get in the store.
It fetches the object and places it on the 'obj' property for its children (this prop will start as null
because the fetch is async). It also ensures that the object is watched while the children are mounted.
*/
const mapStateToProps = (state, ownProps) => ({obj: gets.getObject(state, ownProps.oId)});
function connectObj(Wrapped){
const HOC = React.createClass({
render(){
return <Wrapped {...this.props} />
},
componentDidMount(){
this.fetchAndWatch()},
componentWillUnmount(){
if (isFunction(this._unwatch)) this._unwatch()},
fetchAndWatch(){
const {fetchObject, watchObject, oId} = this.props;
fetchObject(oId).then((obj) => {
this._unwatch = watchObject(oId);
return obj})}});
return connect(mapStateToProps, actions)(HOC)}
export default connectObj;
Then I can use it anywhere thus:
"use strict";
import React from 'react';
import connectObj from 'redux/connect_obj';
const Method = connectObj(React.createClass({
render(){
const {obj, oId} = this.props;
return (obj) ? <p>{obj.id}: {obj.name}/{obj.function}</p> : <p>Fetching {oId}</p>}}));
So connectObj achieves my goal of creating a project wide replacement for setting up the connect explicitly along with a container component to watch/unwatch the objects. This saves quite a lot of boiler plate and gives us a single place to maintain the setup and connection of the store to the components whose job is just to present the objects that may change over time (through updates from the service).
I still don't understand why my first attempt does not work and this workaround does not support injecting other state props (as all the actions are available there is no need to worry about the dispatches).

Try using a different variable name for the component parameter.
const connect = (mapStateToProps, watchObjectId) => (MyComponent) => {
const ContainerComponent = React.createClass({
render() {
return <MyComponent {...this.props} obj={this.state.obj} />
}
...
fetchAndWatch() {
fetchObject(watchObjectId).then(obj => {
this._unwatch = watchObject(watchObjectId);
this.setState({obj});
})
}
});
...
}
I think the problem might be because the component is in lower case (<component {...this.props} />). JSX treats lowercase elements as DOM element and capitalized as React element.
Edit:
If you need to access the obj data, you'll have to pass it as props to the component. Updated the code snippet