JavaScript Interview Question – What is Lexical Scoping and Closures in JavaScript? Part -1
In this article, we will discuss two important concepts in JavaScript – Lexical Scoping and Closures. These are often asked in JavaScript interviews and it is important for every JavaScript developer to have a clear understanding of these concepts.
What is Lexical Scoping?
Lexical scoping, also known as static scoping, is a way of defining the scope of a variable within a block of code. In lexical scoping, the scope of a variable is determined by where the variable is declared in the code.
When a variable is declared inside a function, its scope is limited to that function and any nested functions within it. This means that the variable is only accessible within that particular function and its nested functions.
On the other hand, if a variable is declared outside of any function, it is considered to be in the global scope and is accessible from anywhere in the code.
What are Closures?
Closures are closely related to lexical scoping. A closure is created when a function is defined within another function and the inner function is returned or passed as a value. The inner function has access to the variables declared in the outer function, even after the outer function has finished executing.
This is possible because the inner function maintains a reference to the variables in the outer function’s scope, creating a closure. Closures are often used to create private variables and methods in JavaScript.
For example:
function outerFunction() {
var outerVar = 'I am in the outer function';
function innerFunction() {
console.log(outerVar);
}
return innerFunction;
}
var innerFunc = outerFunction();
innerFunc(); // Output: I am in the outer function
In this example, the innerFunction has access to the outerVar variable, even though it is declared in the outer function. This is because innerFunction forms a closure over the outerFunction, preserving the scope of the variables.
In conclusion, lexical scoping and closures are important concepts in JavaScript that every developer should be familiar with. Understanding these concepts will not only help in interviews but also in writing better and more efficient JavaScript code.
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