Proxy Pattern

A proxy is an object that has the same interface as another object and is used in place of that other object. It provides a surrogate or placeholder for another object to control access to it. It intends to add a wrapper and delegation to protect the real component from undue complexity.

• It allows us to create placeholder wrappers for objects
• A proxy Object allows external access control to the object
• Implements the same interface as the original object

Use cases

• Caching remotely accessed data
• Optimize or pre process data on access
• Logging
• Encryption
• Simulating private and inaccessible properties
• Data validation

// External API Service
function CryptocurrencyAPI() {
  this.getValue = function (coin) {
    console.log('Calling External API...')
    switch (coin) {
      case 'Bitcoin':
        return '$8,500'
      case 'Litecoin':
        return '$50'
      case 'Ethereum':
        return '$175'
      default:
        return 'NA'
    }
  }
}

function CryptocurrencyProxy() {
  this.api = new CryptocurrencyAPI()
  this.cache = {}

  this.getValue = function (coin) {
    if (this.cache[coin] == null) {
      this.cache[coin] = this.api.getValue(coin)
    }
    return this.cache[coin]
  }
}

const proxy = new CryptocurrencyProxy()
console.log(proxy.getValue('Bitcoin'))
console.log(proxy.getValue('Litecoin'))