Coderweekend

What is the difference between var and let in Javascript

In JavaScript, both var and let are used to declare variables.

The let keyword was introduced in ECMAScript 6 (ES6) as an improvement over the var keyword.

What is the difference between var and let in Javascript #

The main difference between var and let is that.

  • var has function-level scoping.
  • let has block-level scoping.

To put it simply, let has the same behavior as most modern programming languages, and I think it is recommended to use in today's JavaScript development.

Here is a longer answer.

  • A variable declared using var is accessible throughout the entire function in which it is declared. You can access it even before the declaration.
  • A variable declared using let is accessible within the block they are declared in. This is the behavior you probably expected.

Here is an example of let and var.

function varExample() {
  console.log(x);
  // print undefined
  if (true) {
    var x = 2;
    console.log(x);
    // print 2
  }

  console.log(x);
  // print 2
}

function letExample() {
  // x is not known here
  // You will get "ReferenceError: x is not defined" error
  // If you trying to reference x
  if (true) {
    let x = 2;
    console.log(x); 
    //print 2
  }
  // x is not known here
}

In the first example using var, the x is declared inside an if block, but we can access its value at the beginning where the value is undefined and after the if block where the value is 2.

In the second example using let, the x can only be used within the if block. Trying to access it elsewhere would cause a "ReferenceError: x is not defined" error. This is the same behavior as most modern programming languages.