What is function expression?
The function keyword can be used to define a function inside an expression.
A function expression is very similar to and has almost the same syntax as, a function declaration.
The main difference between a function expression and a function declaration is the function name, which can be omitted in function expressions to create anonymous functions.
Function expressions in JavaScript are not hoisted, unlike function declarations. You can't use function expressions before you create them
If you want to refer to the current function inside the function body, you need to create a named function expression. This name is then local only to the function body (scope). This avoids using the deprecated arguments.callee property to call the function recursively.