Global variables in JavaScript functions

In JavaScript (most often not in other languages), variables defined outside of a function will be visible inside that function. Such variables are called global. Let's look at an example:

let num = 1; // variable outside the function

function func() {
	console.log(num); // the num variable is visible inside the function
}

func(); // shows 1

In fact, the variable need to be defined not before the definition of the function, but before calling it:

function func() {
	console.log(num);
}

let num = 1; // variable outside the function
func();      // shows 1

If you change the value of the variable and then call the function each time, the alert will give different results each time:

function func() {
	console.log(num);
}

let num; // declare a variable

num = 1; // set the value 1
func();  // shows 1

num = 2; // set the value 2
func();  // shows 2

If we have several functions, then the global variable will be available in each of these functions:

function func1() {
	console.log(num);
}

function func2() {
	console.log(num);
}

let num = 1;

func1(); // shows 1
func2(); // shows 1

If changes occur with a global variable in one function, then this variable will change in all functions using this variable:

function func1() {
	console.log(num);
	num++; // change global variable
}

function func2() {
	console.log(num);
}

let num = 1;

func1(); // shows 1
func2(); // shows 2

Since any of the functions can easily change the global variable, their use is a breeding ground for subtle errors. For this reason, the use of global variables in a script should be kept to a minimum. It is desirable that they do not exist at all or that there is a minimal amount.

Determine what will be output to the console without running the code:

let num = 1;
		
function func() {
	console.log(num);
}

func();

Determine what will be output to the console without running the code:

let num = 1;
		
function func() {
	console.log(num);
}

num = 2;
func();

Determine what will be output to the console without running the code:

function func() {
	console.log(num);
}

let num;

num = 1;
func();

num = 2;
func();