# Nuances of variable scope in if-else constructs in JavaScript

The scope of variables has some nuance. Let's look at it with an example. Let's declare the variable `res` with one value outside our condition, and change this value to another inside the condition:

`let res = 1; if (true) { res = 2; } console.log(res); // shows 2`

As you can see, the variable `res` has changed inside the condition. However, everything will change if the variable `res` is also declared inside the c ondition through `let`:

`let res = 1; if (true) { let res = 2; // declare a variable with let } console.log(res); // shows 1, not 2!`

The thing here is that the declaration of a variable through `let` inside the condition created the local variable `res`.

That is, there is one variable `res` inside the condition, and another one outside it. You can verify this by printing the value of the variable to the console inside the condition:

`let res = 1; if (true) { let res = 2; console.log(res); // shows 2 } console.log(res); // shows 1`

The author of the code below wanted to perform an age validation for reaching of `18` years. The code, however, prints the value `undefined` to the console for any age value. Please fix the code author's mistake. Here is the problematic code:

`let age = 17; let adult; if (age >= 18) { let adult = true; } else { let adult = false; } console.log(adult);`

The author of the code below wanted to perform an age validation for reaching of `18` years. After checking the code, it turned out that if the age is equal to or greater than `18` years, then true is written to the variable `adult`, as it should be, however, if the age is less than `18`, then the variable `adult` has the value `undefined`. Please fix the code author's mistake.

Here is the problematic code:

`let age = 17; let adult; if (age >= 18) { adult = true; } else { let adult = false; } console.log(adult);`

The author of the code below wanted to perform an age checking. The code, however, prints the value `undefined` to the console for any age value. Please fix the code author's mistake.

Here is the problematic code:

`let age = 17; let res; if (age >= 18) { if (age <= 23) { let res = 'from 18 to 23'; } else { let res = 'greater than 23'; } } else { let res = 'less than 18'; } console.log(res);`

The author of the code below wanted to perform an age checking. The code, however, when the age value is greater than `18` years, prints the value `undefined` to the console. Please fix the code author's mistake.

Here is the problematic code:

`let age = 19; let res; if (age >= 18) { let res; if (age <= 23) { res = 'from 18 to 23'; } else { res = 'greater than 23'; } } else { res = 'less than 18'; } console.log(res);`
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