# 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();`
←→
↑
en ru