Global Variables in Javascript

JavaScript is a versatile yet functional language. Variables, which are key to any programming language, can be used to store values that can be accessed at any time. However, when using functions, there are certain factors related to the scope of the function that limit our ability to access a variable.

We cannot access a variable if it is outside the scope of the function, and so the variables we want to use must have the proper scope upon declaration. To avoid issues related to scope, it is important to understand global variables. Therefore, in this article, we are going to discuss global variables and scope.

The scope of a function can be considered as a boundary within which the function can be accessed. However, while a function does not know what is happening beyond the curly brackets that define it, a global variable can be accessed from anywhere in the program.

Syntax

The syntax used to create a global variable, shown below, is no different than that used to create other variables.

var variableName = value

However, the location of this declaration is very important. We will explore this concept more fully by considering some examples.

Example

First, let’s create a function called subtraction.

function subtraction(a,b) {
 var subNum = 23;
}

In this function, we initialized a variable and assigned it a value. Now, we can try to access the variable in another function, i.e., division, and call that function.

function division(a,b) {
 console.log(subNum);
}

division();

However, we get the following reference error because the variable subName is not defined within the correct scope.

This error will occur any time we try to access subNum outside the function in which it is defined. For example:

function subtraction(a,b) {
 var subNum = 23;
};

console.log(subNum);

Here, we still cannot access the variable because it is restricted to the subtraction function.

However, let’s see what happens if we create the variable outside the function—for example, at the beginning of the script:

var globalVar = 11;

Now, let’s try to access it:

console.log(globalVar);

As shown below, we no longer get a reference error.

Furthermore, globalVar should be accessible from any function.

function division(a,b) {
 console.log(globalVar);
}

division();

As you can see below, globalVar is still accessible.

Conclusion

In this article, we explained scope and global variables by using simple examples. We hope you continue learning JavaScript with linuxhint.com.

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