Ready-only Proxy - a read-only view over JS objects

read-only-proxy.js

export const isObject = thing => thing != null && typeof thing === "object"

export class ReadOnlyProxyWriteError extends Error {}

const ReadOnlyProxyDescriptor = {
  get: (target, key) => {
    let value = target[key]
    if (!isObject(value)) {
      return value
    }
    return readonly(value)
  },
  set: (target, key) => {
    throw new ReadOnlyProxyWriteError('Cannot write on read-only proxy')
  },
  deleteProperty: (target, key) => {
    throw new ReadOnlyProxyWriteError('Cannot delete on read-only proxy')
  }
}

// Create a read-only proxy over an object.
// Sub-properties that are objects also return read-only proxies.
export const readonly = obj => new Proxy(obj, ReadOnlyProxyDescriptor)