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# Question 8

### Question

How would you implement a custom range checking function that uses `Number.isFinite()` internally?

### Answer

Here's how you can implement a custom range checking function in JavaScript, incorporating the power of `Number.isFinite()` for robust validation:

```javascript
function isInRange(value, min, max) {
  return Number.isFinite(value) && value >= min && value <= max; 
}

// Examples:
console.log(isInRange(5, 1, 10));    // Output: true (5 is within the range)
console.log(isInRange(20, 1, 10));   // Output: false (20 is outside the range)
console.log(isInRange(-1, 1, 10));  // Output: true (-1 is within the range)
console.log(isInRange(NaN, 1, 10));  // Output: false (NaN is not finite)
```

**Explanation:**

* **`function isInRange(value, min, max)`:** Defines a function named `isInRange` that takes three parameters: the `value` to check, the `min`imum allowed value, and the `max`imum allowed value.
* **`Number.isFinite(value)`:** This crucial step ensures that the input `value` is a finite number before proceeding with any comparisons. If `value` is NaN (Not a Number), infinity, or some other non-finite type, the function immediately returns `false`.
* **`value >= min && value <= max`:** This condition checks if the `value` falls within the specified range, inclusive of both `min` and `max`.

**Key Points:**

* **Robustness:** By using `Number.isFinite()`, this function gracefully handles potential issues with invalid input types (like NaN), preventing unexpected behavior.
* **Readability:** The code is clear and concise, making it easy to understand its purpose and how it works.