extract version from package.json with bash inside jenkins pipeline

Script in package.json:

"scripts": {
    "version": "echo $npm_package_version"
  },

One of the stage in Jenkins pipeline:

stage('Build'){
    sh 'npm install'
    def packageVersion = sh 'npm run version'
    echo $packageVersion
    sh 'VERSION=${packageVersion} npm run build'
}

I got version from npm script output, but following line

echo $packageVersion

return null

Is packageVersion value not correctly assigned?

Edited: when using Pipeline Utility Steps with following code

stage('Build'){
    def packageJSON = readJSON file: 'package.json'
    def packageJSONVersion = packageJSON.version
    echo packageJSONVersion
    sh 'VERSION=${packageJSONVersion}_${BUILD_NUMBER}_${BRANCH_NAME} npm run build'
        }

I get

[Pipeline] echo
1.1.0
[Pipeline] sh
[...] Running shell script + VERSION=_16_SOME_BRANCH npm run build

So I am able to extract version, but still cannot pass it when running script

After your edit using readJSON, you now get string interpolation wrong. Variables within single quotes are not replaced in Groovy, only within double quotes.

sh 'VERSION=${packageJSONVersion}_${BUILD_NUMBER}_${BRANCH_NAME} npm run build'

must be

sh "VERSION=${packageJSONVersion}_${BUILD_NUMBER}_${BRANCH_NAME} npm run build"