higher-order-function-js-intro.rb

/* Simple function that calculates tax for a certain amount */
const calculateTax = function(amount, taxRate){
  return amount * taxRate;
}




/* 
   Straightforward Higher Order Function that prepends a currency symbol to 
   a function.
*/
const prependCurrencySymbol = function(someFunction, symbol = "$"){
  
  /* 
    Builds an augmented version of the "someFunction" provided that 
    append the currency symbol 
  */
  const modifiedFunction = function(...args){
    return `${symbol}${someFunction(...args)}`;
  }
  
  /* Return a new function that is the augmented version of the original function */
  return modifiedFunction;
}


/* 
  These function use our higher order function to modify and customize the  
  behaviour of the original function "calculateTax"
*/
const calculateTaxWithDollarSymbol = prependCurrencySymbol(calculateTax, "$")
const calculateTaxWithPoundSymbol = prependCurrencySymbol(calculateTax, "£")


calculateTax(10, 0.14)
// 1.4000000000000001

calculateTaxWithDollarSymbol(10, 0.14)
// "$1.4000000000000001"

calculateTaxWithPoundSymbol(10, 0.14)
// "£1.4000000000000001"