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After I create a sample react app using create-react-app, npm start fails.

I have tried this using node 11.4 and 10.4 (npm 6.4.1)

>npm install create-react-app -g

>create-react-app t2

>cd t2

>npm start

expected: to be able to start simple react server to hit in browser at localhost:3000

actual: server did not start, got this in my terminal
Salvatores-iMac:t2 samr$ npm start

t2@0.1.0 start /Users/samr/dev/githubs/react/t2
react-scripts start

/Users/samr/dev/githubs/react/t2/node_modules/ajv/lib/keyword.js:65
throw new Error('custom keyword definition is invalid: ' + this.errorsText(validateDefinition.errors));
^

Error: custom keyword definition is invalid: data.errors should be boolean
at Ajv.addKeyword (/Users/samr/dev/githubs/react/t2/node_modules/ajv/lib/keyword.js:65:13)
at module.exports (/Users/samr/dev/githubs/react/t2/node_modules/ajv-errors/index.js:10:7)
at Object. (/Users/samr/dev/githubs/react/t2/node_modules/schema-utils/src/validateOptions.js:22:1)
at Module._compile (internal/modules/cjs/loader.js:723:30)
at Object.Module._extensions..js (internal/modules/cjs/loader.js:734:10)
at Module.load (internal/modules/cjs/loader.js:620:32)
at tryModuleLoad (internal/modules/cjs/loader.js:560:12)
at Function.Module._load (internal/modules/cjs/loader.js:552:3)
at Module.require (internal/modules/cjs/loader.js:659:17)
at require (internal/modules/cjs/helpers.js:22:18)
npm ERR! code ELIFECYCLE
npm ERR! errno 1
npm ERR! t2@0.1.0 start: react-scripts start
npm ERR! Exit status 1
npm ERR!
npm ERR! Failed at the t2@0.1.0 start script.
npm ERR! This is probably not a problem with npm. There is likely additional logging output above.

npm ERR! A complete log of this run can be found in:
npm ERR! /Users/samr/.npm/_logs/2019-02-09T23_19_40_848Z-debug.log

Quick fix is mentioned here https://github.com/webpack/webpack/issues/8768

Essentially go to node_modules/ajv/lib/keyword.js and comment out lines 64 and 65.

As @atsnam has said, you can find the resolution here https://github.com/webpack/webpack/issues/8768.

If you use yarn

add below to package.json

"resolutions": {

  "ajv": "6.8.1"

}

then run yarn install

if you use npm

npm uninstall ajv

npm install ajv@6.8.1

That worked for me

I'm running into this as well. Npm start worked fine for me for an app I created last night, but today I tried to use create-react-app for a new project, and in the new project npm start is not working for me.

Copying over my node_modules folder from my previous app did help as a temporary workaround, but once I tried installing react router into my new app and then running npm start, I'm running into this error once again.

same here, maybe you can check this https://github.com/webpack/webpack/issues/8768, changing the file in file node_modulesajv-errorsindex.js as someone says here solved it for now as a quick fix

As per the suggestion in Github answers the below change has enabled me to work.

To fix this error, just change:

Line 14: `errors: 'full',`

to:

Line 14: `errors: true`

in file **node_modulesajv-errorsindex.js**

I am getting the same error
this worked for me

just add

  "resolutions": {

    "ajv": "6.8.1"

  }

to your package.json

if you use yarn:
run yarn install