crappyStore.js

const l = localStorage

const crappyStore = {
  get: (key) => JSON.parse(l.getItem(key)),
  set: (key, data) => l.setItem(key, JSON.stringify(data)),
  rm: (key) => l.removeItem(key),
  getKeysFor: (prefix) => {
    const ret = []
    for (let key in l) {
      ret.push(key)
    }

    return ret.filter((c) => c.substring(0, prefix.length) == prefix)  
  }
}

// Usage Example

const store_prefix = 'user_'
const userId = '123456'

crappyStore.set(store_prefix + userId, {name: 'Klaus'})
crappyStore.get(store_prefix + userId)

const allUserKeys = crappyStore.getKeysFor(store_prefix)

allUserKeys.map(userKey => {
  const user = crappyStore.get(userKey)
  console.info(user.name)
})