JavaScript difference between var and let

JavaScript has two ways of declaring variables: using the "var" keyword and the "let" keyword. Both are used to create variables, but they have some important differences that you should be aware of when writing JavaScript code. In this tutorial, we will cover the main differences between "var" and "let" in JavaScript, and help you decide which one to use in different situations.

The first main difference between "var" and "let" is their scope. "var" variables are function-scoped, which means that they are accessible within the entire function in which they are declared. On the other hand, "let" variables are block-scoped, which means that they are only accessible within the block in which they are declared. This means that "let" variables are only accessible within a specific section of your code, and cannot be accessed outside of that section.

1if(true){
2    var x = 10;
3    let y = 20;
4}
5console.log(x); //10
6console.log(y); //ReferenceError: y is not defined

Another difference between "var" and "let" is that "var" variables are hoisted to the top of their scope, while "let" variables are not. This means that when you use "var" to declare a variable, you can access it before you declare it in your code. However, with "let" variables, you cannot access them before they are declared.

1console.log(x); //undefined
2var x = 10;
3console.log(y); //ReferenceError: y is not defined
4let y = 20;

A third difference between "var" and "let" is that "let" variables cannot be declared multiple times in the same scope. This is known as the "Temporal Dead Zone" and it is a feature of "let" variables that prevent them from being declared multiple times. On the other hand, "var" variables can be declared multiple times in the same scope.

1let x = 10;
2let x = 20; //SyntaxError: Identifier 'x' has already been declared
3var y = 10;
4var y = 20; //No error

"var" and "let" are both used to create variables in JavaScript, but they have some important differences that you should be aware of. "var" variables are function-scoped, while "let" variables are block-scoped. "var" variables are hoisted to the top of their scope, while "let" variables are not. "let" variables cannot be declared multiple times in the same scope, while "var" variables can. "let" is the recommended keyword for variable declaration as it gives more control over variable scope and prevents variable redeclaration.