Obligatory: SHA1 is broken, you can compute SHA1 collisions for 45,000 USD. You should use sha256:
var getSHA256ofJSON = function(input){
return crypto.createHash('sha256').update(JSON.stringify(input)).digest('hex')
}
To answer your question and make a SHA1 hash:
const INSECURE_ALGORITHM = 'sha1'
var getInsecureSHA1ofJSON = function(input){
return crypto.createHash(INSECURE_ALGORITHM).update(JSON.stringify(input)).digest('hex')
}
Then:
getSHA256ofJSON('whatever')
or
getSHA256ofJSON(['whatever'])
or
getSHA256ofJSON({'this':'too'})