- Global Scope – Scope outside the outermost function attached to Window
- Local Scope – Inside the function being executed
Let’s look at the code below. We have a global variable defined in first line in global scope. Then we have a local variable defined inside the function fun().
When we execute the function fun(), the output shows that both global as well as local variables are accessible inside the function as we are able to console.log them. This shows that inside the function we have access to both global variables (declared outside the function) and local variables (declared inside the function).Let’s move the console.log statements outside the function and put them just after calling the function.
We are still able to see the value of global variable, but for local variable console.log throws an error. This is because now the console.log statements are present in global scope where they have access to global variables but cannot access the local variables.
Word of caution: Whenever you are declaring variables, always use the prefix var. If you don’t use the var keyword, then the variables are by default created in the global scope. For instance, in the above example, let’s just remove the keyword var before the declaration of localVar.
What if we want to access the global variable instead of local one here. Well, the window object comes to our rescue. All the global variables are attached to window object and thus we can access the global variable name as shown in example below.
In the first example as we didn’t use the keyword var, the variable “i” was assumed to be declared in global scope and thus the output was 100. In the second example, “i” became a local variable and thus was not accessible outside the scope of that function.
In the above code, you have a variable “name” which acts as a private variable as it is not directly accessible outside the scope of function person(). But the variable “name” is accessible by the functions inside the scope of function person(). This lets us create the getter and setter function to access the variables, thereby implementing the data hiding concept of classes in OOPS.
About the author:
“Harshit is a technology enthusiast and has keen interest in programming. He holds a B.Tech. degree in Computer Science from JIIT, Noida and currently works as Front-end Developer at SAP. He is also a state level table tennis player. Apart from this he likes to unwind by watching movies and English sitcoms. He is based out of Delhi and you can reach out to him at https://in.linkedin.com/pub/harshit-jain/2a/129/bb5
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