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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.<anonymous> (/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

just add resolutions to your package.json like this:

 
 "dependencies": 
 ...
 
 "resolutions": 
 "ajv": "6.8.1"
 
 

then run npm install. if you use yarn, yarn install

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**