strategy_pattern.js

function Fedex()
{
  this.calculate = ({ weight }) => {
    return weight * 2.45;
  }
}

function UPS()
{
  this.calculate = ({ weight }) => {
    return weight * 1.56;
  }
}

function USPS()
{
  this.calculate = ({ weight }) => {
    return weight * 4.5;
  }
}

function Shipping()
{
  this.company = "";
  this.setStrategy = (company) => {
    this.company = company;
  }
  this.calculate = package => {
    return this.company.calculate(package);
  }  
}

const fedex = new Fedex();
const ups = new UPS();
const usps = new USPS();
const package = { from: "Alabama", to: "Georgia", weight: 2 };

const shipping = new Shipping();
shipping.setStrategy(fedex);
console.log("Fedex: " + shipping.calculate(package));

shipping.setStrategy(ups);
console.log("UPS: " + shipping.calculate(package));

shipping.setStrategy(usps);
console.log("USPS: " + shipping.calculate(package));