incrementer.js

// *** Functional Programming: Avoid Mutations and Side Effects Using Functional Programming ***

// If you haven't already figured it out, the issue in the previous challenge was with the splice
//  call in the tabClose() function. Unfortunately, splice changes the original array it is called 
//  on, so the second call to it used a modified array, and gave unexpected results.

// This is a small example of a much larger pattern - you call a function on a variable, array, 
// or an object, and the function changes the variable or something in the object.

// One of the core principle of functional programming is to not change things. Changes lead to 
// bugs. It's easier to prevent bugs knowing that your functions don't change anything, including 
// the function arguments or any global variable.

// The previous example didn't have any complicated operations but the splice method changed 
// the original array, and resulted in a bug.

// Recall that in functional programming, changing or altering things is called mutation, and
// the outcome is called a side effect. A function, ideally, should be a pure function, meaning
// that it does not cause any side effects.

// Fill in the code for the function incrementer so it returns the value of the global variable
// fixedValue increased by one.


// the global variable
var fixedValue = 4;

function incrementer () {
  // Add your code below this line
  let val = fixedValue;
  return val + 1;
  
  // Add your code above this line
}

var newValue = incrementer(); // Should equal 5
console.log(fixedValue); // Should print 4