What is the difference between closure and block scope in JavaScript?

What is the difference between closure and block scope in JavaScript?

In JavaScript, closure is a feature where an inner function has access to the outer function's variables even after the outer function has executed. Block scope, on the other hand, refers to the scope created by curly braces (like in if statements or loops), where variables declared with let and const are only accessible within that block.

Can you give me an example of closure?

Sure! Here's a simple example:

function outerFunction() {
    let outerVariable = 'I am outside!';
    function innerFunction() {
        console.log(outerVariable);
    }
    return innerFunction;
}

const myInnerFunction = outerFunction();
myInnerFunction(); // Outputs: I am outside!

In this example, innerFunction has access to outerVariable even after outerFunction has finished executing.

What about block scope? Can you show me that?

Absolutely! Here's an example of block scope:

if (true) {
    let blockScopedVariable = 'I am inside a block!';
    console.log(blockScopedVariable); // Outputs: I am inside a block!
}

console.log(blockScopedVariable); // ReferenceError: blockScopedVariable is not defined

In this case, blockScopedVariable is only accessible within the if block, and trying to access it outside results in an error.

How do closures help in JavaScript?

Closures are useful for data encapsulation, allowing you to create private variables and functions. They enable you to maintain state in asynchronous programming and are often used in functional programming patterns.