JavaScript Interview Ep # 1 – What is function expression and declaration

There are three ways a JavaScript function can be created. They are as follows:

1. Function declaration
2. Function expression
3. Arrow function

When you create a function as a declaration or statement, it gets hoisted at the top of the execution context and can be used before it is made. Example below:

console.log(Foo());
function Foo(){

  return "Returned from function Foo";
}

When you create a function as an expression, it does not get hoisted at the top of the execution context and cannot be used before it is made. Example below:

console.log(Koo); // error 
var Koo = function Koo(){
  return "Return from function Koo";
}

Watch the full explanation in the video here: