freeCodeCamp/guide/english/certifications/javascript-algorithms-and-data-structures/functional-programming/avoid-mutations-and-side-effects-using-functional-programming/index.md

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title: Avoid Mutations and Side Effects Using Functional Programming
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# Avoid Mutations and Side Effects Using Functional Programming

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## Problem Explanation

Fill in the code for the function `incrementer` so it returns the value of the global variable `fixedValue` increased by one. `fixedValue` should not change, no matter how many times the function `incrememter` is called.


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## Hints

### Hint 1

Using the increment operator (`++`) on `fixedValue` will mutate `fixedValue`, meaning it will no longer reference the same value it was assigned with. 


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## Solutions

<details><summary>Solution 1 (Click to Show/Hide)</summary>

```javascript
// the global variable
var fixedValue = 4;

function incrementer() {
  // Add your code below this line
  return fixedValue + 1;

  // Add your code above this line
}

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