The var keyword

Before ES6, all variables in JavaScript were declared with the var keyword. This keyword causes our variables to have a function scope.

Lets understand this better with the following code snippet:

  function SayName(){
   var name = "Tega";
   }

console.log(name)//Undefined

The console prints out undefined because the variable name inside the SayName function is not visible outside the SayNamefunction.

The behaviour is quite different in another block that is not a function block. For example, see what happens in an if block.

  if(true){
   var name = "Tega";
   }

console.log(name)//Tega

The console prints Tega.

Considering the results from the two examples, it is evident that variables declared with the var keyword have a local scope only when they are found within a function block.

It's a bad behaviour
This is a bad behaviour that has caused a lot of frustration amongst JavaScript programmers. Prior to ES6, JavaScript had function scope, but block scoping is more common in most programming languages. With ES6, let and const keywords were introduced to allow us to declare variables that are block scoped which is a safe behaviour.

Thank you for reading!
Happy Coding!❤