Javascript :: Functions within Functions

FunctionsWithinFunctions1.js

// returning price + shipping and salesTax
function billerBuilder(state) {
  return function(price) {
    if (state === 'NY') {
      return price * 1.03 * 1.04;
    }
    return price * 1.05 * 1.06625;
  }  
}




// times tables
function timesTable(num1) {
  return function(num2) {
    return num1 * num2;
  }
}

// or can write it like this: (num followed by arrow indicates a function)
const timesTable = multiplier => num => num * multiplier;



// passing in two arguments (where callback is a function)
function partial(callback, argA) {
  return (argB) => {
    return callback(argA, argB);
  }
}



// subfunction counts the number of times function has been called (must define count in outer scope for closure)
function callCount() {
  let count = 0;
  return function() {
    count ++;
    return count;
  }
}






// function to string
function stringify(callback) {
  return function newfunction() {
    let value = '';
    return callback(value).toString();
  }
}
// or like this:
function stringify(callback) {
  return function() {
    return callback().toString();
  }
}

// or can do it like this:
const stringify = (callback) => {
    return () => {
        return `${callback()}`;
    }
}


// using a cache
function cacheSavings(callback) {

  // create an object to store the returned values
  // the keys will be the arguments given to the callback
  // the values will be the returned value from the callback
  let cache = {};

  return function(argument) {

    // if the argument is not a key in the cache already...
    if (!(argument in cache)) {

      // ...call the callback and get the result
      let callbackResult = callback(argument);

      // then, add the argument and result to the cache
      cache[argument] = callbackResult;
    }

    // return the cached value
    return cache[argument];
  }
}

// written the other way:
const cacheSavings = (callback) => {
    const cache = {};
    
    return (arg) => {
        if (cache[arg]) {
            return cache[arg];
        }
        
        const result = callback(arg);
        cache[arg] = result;
        return result;
    }
}