Hoisting of var

Hoisting is a JavaScript mechanism where variables and function declarations are moved to the top of their scope before code execution. This means that if we do this:

console.log (greeter);
var greeter = "say hello"

it is interpreted as this:

var greeter;
console.log(greeter); // greeter is undefined
greeter = "say hello"

So var variables are hoisted to the top of their scope and initialized with a value of undefined.