Understanding JavaScript Variables and Functions: Scope of Variables and Functions in JavaScript
Published: 2022-11-09 15:06:37



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When you first learn about variables and functions in the world of coding, it can feel like a foreign language. It’s hard to know where to begin because there are so many different things to cover! Variables and functions are two crucial concepts in coding, especially when learning JavaScript. These two elements are essential for creating efficient programs that store and reuse data effectively. In this blog post, we’ll go through everything you need to know about JavaScript variables and functions, as well as their scope in this programming language.


**What Are JavaScript Variables?**
A variable is a placeholder in your code for a value, just like how a pencil is a placeholder for writing on paper. Variables store information while your program is running. This means that later on when you need to use the information stored in the variable, the variable will be there to help you out. A variable is made up of a few parts, including a name, a type, and an identifier. Let’s break these down one by one. - Name: The name of your variable is what you’ll see in your code. It’s what tells you what the variable is used for. Keep in mind that variable names are case-sensitive. This means that “myName” and “myname” are treated as two different variables. - Type: The type of your variable tells the computer what kind of information is allowed in that variable. Does it need to be a number? A string of letters? A boolean (true/false) value? Or something else? For example, you can use a variable to store an email address, a name, or the current date and time. You’ll need to let the computer know what type of information is allowed in that variable by choosing a data type. - Identifier: The identifier of your variable is a name that you’ll use in your code. It can’t start with a number, and it can’t use any special characters (like $, %, or *. The best practice is to use letters, numbers, and the underscore character. The identifier can be as long as you want, but it’s best to make it short and simple. You’ll want it to be easy to recognize and remember.

**Understanding Variable Scope in JavaScript**
Scoping is a term used to describe how a variable is accessible in your code. Variable scope is dependent on how and where the variable was created, and it determines where that variable can be used in your code. - Global variables: If you create a variable outside of any function, it’s considered a global variable. This means that the variable is accessible anywhere in your code. You might use a global variable if you want to store information that you need in every function. But note that this also makes the global variable available to any other code that runs on the same webpage. Global variables are generally considered a bad practice because they can lead to code that’s difficult to maintain. - Local variables: If you create a variable inside a function, it’s a local variable. This means that the variable can only be seen by the code that’s inside that function. You might want to use a local variable to store data that you only need to use inside that function. Local variables are often used to store intermediate calculations, since you don’t need to use them outside the function.

**Defining Functions in JavaScript**
A function is a piece of code that can be executed by your program. Consider a function like a self-contained mini-program that can be reused in your code. You can use functions to execute code that you often use, like validating user inputs or calculating averages. This will help you keep your code organized and make it easier to read and understand. There are many different ways to define a function in JavaScript. - function name(): You can define a function by typing function name, followed by parenthesis (). You’ll then write out the code you want executed in the function, followed by a closing parenthesis. The function name is what you’ll use to call the function in your code. - function name(parameters): Another way to define a function is to include parameters inside the parenthesis. A parameter is a piece of information that can be used in the function. You can also use a parameter to receive information from the function. You’ll need to create a variable that matches the parameter name before using it in the function.

**Functions in JavaScript with no Variable Scope**
Now that we’ve covered how functions work in JavaScript, we’re ready to dive into function scopes. Remember, functions have a variable scope, which means that the variables created inside a function are only visible inside that function. When defining functions, you have two options with regard to variable scopes. You can either create a new variable scope for the function, or you can use the parent scopes for the variables. - New variable scopes: If you want a new variable scope for the function, you’ll need to declare the variables inside the function and give them a data type. After the function finishes executing, the variables will be removed from memory. This means that you can’t use these variables outside the function. - Parent variable scopes: You can also use the parent scopes for the variables. This means that the variables will be visible in the function, as well as in any other function that uses the same variable. Keep in mind that the variable can be used any place where the function is called (parent scopes).

**Confusion with JavaScript Scoping**
The difference between new scopes and parent scopes can be confusing, especially because JavaScript also uses a closure. A closure is when a function remembers and uses the scopes outside its own function. A closure is like someone remembering what they ate for dinner the night before. This is done using an identifier in your code called the closure variable, which can refer to the parent scopes. The closure variable is one of those variables that you declare inside a function but don’t give a data type. It’s considered a mistake to use a closure variable since it can lead to code that’s difficult to understand and debug.

**Summing up**
Function scopes are a very important concept in JavaScript, especially when it comes to avoiding confusion with variable scopes. The best practice is to always use new scopes for functions. If you want to share variables between functions, you need to use parent scopes. Now that you understand the concepts behind variables and functions, you’re ready to start creating more efficient JavaScript code. Remember that variables store information while functions execute code. And when you use these in your code, you need to make sure that they follow variable scope rules.