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

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

In JavaScript, function scope means that variables are accessible only within the function they are declared in. Block scope, introduced in ES6, allows variables to be limited to the block (enclosed by curly braces) they are defined in.

Can you give me an example of each?

Sure! For function scope:

function example() {
    var x = 10; // function scoped
    console.log(x);
}
example(); // Outputs: 10
console.log(x); // ReferenceError: x is not defined

For block scope:

if (true) {
    let y = 20; // block scoped
    console.log(y);
}
console.log(y); // ReferenceError: y is not defined

What happens if I use var inside a block?

If you use var inside a block, the variable will still be function scoped. For example:

if (true) {
    var z = 30; // function scoped
}
console.log(z); // Outputs: 30

Are there any best practices for using scope in JavaScript?

Yes! It's generally recommended to use let and const for block scope to avoid unintended variable hoisting and to keep your code cleaner and more predictable.