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I get an error when using the command "npm run start" for my react project

I am new to coding and would appreciate some help with this I get the following error when I try to run my react app: npm run start
Failed to compile.
Loading PostCSS "postcss-normalize" plugin failed: Cannot find module 'postcss-normalize'
Require stack:
/Users/abc/node_modules/postcss-loader/dist/utils.js
/Users/abc/node_modules/postcss-loader/dist/index.js
/Users/abc/node_modules/postcss-loader/dist/cjs.js
/Users/abc/node_modules/loader-runner/lib/loadLoader.js
/Users/abc/node_modules/loader-runner/lib/LoaderRunner.js
/Users/abc/node_modules/webpack/lib/NormalModule.js
/Users/abc/node_modules/webpack-manifest-plugin/dist/index.js
/Users/abc/node_modules/react-scripts/config/webpack.config.js
/Users/abc/node_modules/react-scripts/scripts/start.js
(#/Users/abc/node_modules/bootstrap/dist/css/bootstrap.css)
ERROR in ./node_modules/bootstrap/dist/css/bootstrap.css (./node_modules/css-loader/dist/cjs.js??ruleSet[1].rules[1].oneOf[5].use[1]!./node_modules/postcss-loader/dist/cjs.js??ruleSet[1].rules[1].oneOf[5].use[2]!./node_modules/source-map-loader/dist/cjs.js!./node_modules/bootstrap/dist/css/bootstrap.css)
./node_modules/bootstrap/dist/css/bootstrap.css (./node_modules/css-loader/dist/cjs.js??ruleSet[1].rules[1].oneOf[5].use[1]!./node_modules/postcss-loader/dist/cjs.js??ruleSet[1].rules[1].oneOf[5].use[2]!./node_modules/source-map-loader/dist/cjs.js!./node_modules/bootstrap/dist/css/bootstrap.css)
Module Error (from ./node_modules/postcss-loader/dist/cjs.js):
Loading PostCSS "postcss-normalize" plugin failed: Cannot find module 'postcss-normalize'
Require stack:
/Users/abc/node_modules/postcss-loader/dist/utils.js
/Users/abc/node_modules/postcss-loader/dist/index.js
/Users/abc/node_modules/postcss-loader/dist/cjs.js
/Users/abc/node_modules/loader-runner/lib/loadLoader.js
/Users/abc/node_modules/loader-runner/lib/LoaderRunner.js
/Users/abc/node_modules/webpack/lib/NormalModule.js
/Users/abc/node_modules/webpack-manifest-plugin/dist/index.js
/Users/abc/node_modules/react-scripts/config/webpack.config.js
/Users/abc/node_modules/react-scripts/scripts/start.js
(#/Users/abc/node_modules/bootstrap/dist/css/bootstrap.css)
Thank you so much
I've tried updating to the latest version of node and npm, however, that did not help. I've also verified my code several times as I'm mostly practicing along with a course. Thank you.

As it appears this error will temporarily get fixed by installing the latest version of Node.js.
So to fix this follow these steps:
Download and install the latest Node.js version (recommended for most users, which is 16.15.0 at this moment).
Delete your node_modules directory from your project. Then you can optionally clear npm cache with npm cache clean and verify it with npm cache verify.
Delete package-lock.json/yarn.lock file.
Reinstall all of the dependencies and create a new dependency tree using one of the following commands: npm i/npm install/yarn/yarn install.
Note1: If in any case, you use node-sass in React projects yet, it is recommended to use sass instead.
Note2: In some cases skipping step 1 will also work as expected, but I recommend upgrading the Node.js version if you do not have other dependencies to prevent that.
Note3: As #IvaniltonBezerra mentions in the comments, some app builds may throw errors, since upgrading Node.js to its latest version will upgrade the npm as well it may not compatible with your current dependency tree in production, so to prevent such a problem you have to use --legacy-peer-deps to restore the old behaviour of the old dependencies.
Update
This is now seem to be permanently solved in PostCSS Preset Env and following the above steps with skipping step 1 will also solve the problem.

Error: Unable to resolve module `#react-native-community/toolbar-android`

Weirdly, the react-native-vector-icons was working well but by using ^ ("^6.6.0") for its version in the package.json file on the new release this error happens.
It's weird because two days ago it works well but now starting of my project ran to this error:
error: Error: Unable to resolve module #react-native-community/toolbar-android from node_modules\react-native-vector-icons\lib\toolbar-android.js: #react-native-community/toolbar-android could not be found within the project.

After reading this issue and trying many solutions I reach to two solutions:
You can delete all node_modules folder and put the version of react-native-vector-icons to "6.6.0" instead of "^6.6.0" and then install all packages again. absolutely, it is better to delete all caches and builds and start everything again. (NOT Recommended)
You can install the #react-native-community/toolbar-android by using the below command:
yarn add #react-native-community/toolbar-android
Or
npm install --save #react-native-community/toolbar-android
Note: Both of these solutions are temporary and soonly this bug will be fixed and there is no need to install the toolbar-android package.
Prev Update
I update the package to the version "^7.0.0" on my project and still, the issue is remaining, so this solution is currently perseverance.
New Update
this issue is fixed on version "^7.1.0" and there is no need to install the #react-native-community/toolbar-android.

Update the library
react-native-vector-icons
to the latest version.

I had this problem too.
In my case, only works when I removed and added the package again with the latest version (7.0.0).
yarn remove react-native-vector-icons
yarn add react-native-vector-icons

Had this EXACT same error. All I had to do was install toolbar-android & voilà!
npm install --save #react-native-community/toolbar-android

Go the path \node_modules\native-base\node_modules\react-native-vector-icons\lib\toolbar-android.js
Replace import ToolbarAndroid from '#react-native-community/toolbar-android' to import {ToolbarAndroid} from './react-native';

I also got the same error after upgrading from version 6 to 7. The issue can be fixed simply by resetting the cache.
Please try npm start -- --reset-cache

do this:
rm -rf node_modules/
rm -rf package.lock.json
npm i
react-native start --reset-cache
from your project directory:)

Just Import it direct from react native it solves my problem
node_modules\react-native-vector-icons\lib\toolbar-android.js
import { ToolbarAndroid } from 'react-native';

Same issue, I solved it:
My environment:
RN: 0.61.5
Node: v12.18.3
OS: Windows 10 Pro
You can install react-native-vector-icons latest version (current 7.0.0).
And do not run auto-link (react-native link react-native-vector-icons)
Finally, running react-native start --reset-cache
Good luck.

First let's understand the standard convention used in package.json for packege's version.
So if you see ~1.0.2 it means to install version 1.0.2 or the latest patch version such as 1.0.4. If you see ^1.0.2 it means to install version 1.0.2 or the latest minor or patch version such as 1.1.0.
Now, coming to the issue.
The issue is caused because you are having a version of react-native-vector-icons which is giving you some trouble.
Check it's version by this command under your project directory:
npm list react-native-vector-icons --version \ is it 6.6.0 ??
No ?? . There is the problem. You need strictly 6.6.0 but you got something else.
Solution:
Delete node_modules directory under your project. Change the version of react-native-vector-icons in package.json to 6.6.0 (basically remove ^ to tell npm to get me exactly what I want. Nothing more, nothing less !)
Then do npm install !

The other alternative is to use expo's vector Icons. Something like this.
import { Ionicons } from "#expo/vector-icons".
Then render your Icon like this;
<Ionicons
name="ios-exit-outline"
color={colors.danger}
size={28}
style={{ marginRight: -15 }}
/>

Edit this file node_modules\react-native-vector-icons\lib\toolbar-android.js
remove 'import ToolbarAndroid from '#react-native-community/toolbar-android';'
edit return null

for this case you have not toolbar-android in your modules file and as friends saying you can fix it by this command
windows users:
npm install --save #react-native-community/toolbar-android
Mac users:
yarn add #react-native-community/toolbar-android
But IN GENERAL: I wanna tell you an experience for you guys whenever you encounter with this kind of errors that start with "Unable to resolve module" .
if you have a look to the error we have a problem with the module that system is telling us.
if you have not that module . you can install it with the commands
Windows users:
npm install --save THE MODULE(attention: THE MODULE IS THE NAME OF PACKAGES OR MODULES that u need to install)
and Mac users:
yarn add THE MODULE(attention: THE MODULE IS THE NAME OF PACKAGES OR MODULES that u need to install)
for example lets look at this error:
error Unable to resolve module `#react-native-community/slider` from `App.js`: #react-native-community/slider could not be found within the project.
as you can see error is telling us this module could not be found within our project.
so we need install it with this command:
for windows programmers:
npm install --save #react-native-community/slider
and for mac programmers:
yarn add #react-native-community/slider
that's all.
I hope you understand me clearly and do not have problem with unable to resolve module errors and my command be useful for you.
best regards
Mehrad Karampour (MEH)

Installing react gives the following error

First, I make this globally, then I install my app.
Then I go to my project directories. Finally, when I am running the project it shows the error illustrated in the image below.
I have tried so many thing like uninstalling node.js then reinstalling again or deleting node module(s), etc. What more do you think, should I try? Thank you in advance.
Project is running at http://192.168.0.101/

Downgrading the react-script version to 2.1.8.
npm install react-scripts#2.1.8
npm start
Package json dependencies should get updated to
"dependencies": {
------------------
---------------------
"react-scripts": "2.1.8"
},

ENOLOCAL: can't find package.json file after publishing npm package

Ecosystem
using npm#6.1.0
using node#v8.11.1
Context
I have a JS project that includes a local dependencie :
package.json :
"dependencies": {
"my_local_module": "file:my_local_module"
},
Then, I published the project as npm private package : so far everything is OK.
Issue
When I try to install my private package, I have this issue :
33 error code ENOLOCAL
34 error Could not install from "node_modules\#my_scope\my_project\my_local_module" as it does not contain a package.json file.
Of course, the package.json file exists. When I try to copy manually the project from gitHub instead of installing it with npm, it works perfectly fine but I really would like to make it works with :
npm install #my_scope\my_project
Is there a specific way to publish packages when they include local dependencies or anything like that ? Thank you for your help.

You can try to delete your package-lock.json file
I had the same problem and error. The package-lock.json was still doing a reference to "file:my_local_module".
I deleted it and re npm installed the module to make it work

I found a report of a similar issue within the npm cli github
https://github.com/npm/cli/issues/1756
It appears this may be an issue with npm v6 (I was using version 6.14.12). Updating npm to v7 seems to have solved this issue for me.

package.json dependencies exact version not working

This is an excerpt from my package.json:
"dependencies": {
[...]
"jquery": "2.2.3",
[...]
}
According to the package.json documentation ("must match version exactly") it should get jQuery with version 2.2.3 when you do npm install.
So I was surprised when I found that in my node_modules/jquery/dist folder there is a jquery.js file which says: jQuery JavaScript Library v3.0.0 (Which, of course, broke some of my code)
What happened here? Is this a bug? Is this intended behaviour because some other dependency has a jQuery#3.0.0 sub-dependency?
Same occurs when I put the caret in front of the version number ("jquery": "^2.2.3"). Could not find anything about this in the docs, on SO or on google, so any help will be appreciated.

Do you have a npm-shrinkwrap.json file, which makes npm ignore all changes to your package.json dependencies (devDependencies are not affected) and has a hardcoded jquery#3.0.0 version?
Delete that file and run npm install again.
If you need to, run npm shrinkwrap again afterwards to re-create the shrinkwrap file with the new version numbers.
See documentation here: https://docs.npmjs.com/cli/shrinkwrap