ES6 Proxy Set

es6-proxy-set.js

/**
 * Demo for https://twitter.com/joelnet/status/1163820524709076992
 */

class Person {
  constructor(firstName, lastName) {
    this.firstName = firstName;
    this.lastName = lastName;
  }
}

// ✨✨✨ Wrap new Person in a Proxy ✨✨✨
const proxy = new Proxy(
  new Person('C#', 'Joel'),
  stringValidator('firstName', 'lastName')
)

// 👌 Everything is okay
proxy.firstName = 'JavaScript'
console.log(proxy)

// ⛔ Assignment has been rejected
proxy.lastName = null

/**
 * Validates properties are non-empty string
 */
function stringValidator(...props) {
  return ({
    set(target, name, value) {
      if (props.includes(name)) {
        if (value == null || value == '') {
          throw new TypeError(`${name} cannot be blank`)
        }
        if (typeof value !== 'string') {
          throw new TypeError(`${name} does not support type "${typeof value}". Must be a "string".`)
        }
      }

      target[name] = value
      return true
    }
  })
}