What are the advantages / disadvantages for creating a top-level function in ES6 with or without arrows?

Question

What are the advantages / disadvantages for creating a top-level function in ES6 / ES2015 in different ways? Or is it just a matter of taste / style guidance, etc.

Option 1:

function square(n) {
   return n * n;
}

Option 2:

var square = function(n) {
  return n * n;
};

Option 3:

var square = (n) => {
   return n * n;
};

Option 4:

const square = (n) => {
   return n * n;
};

Answer 1

Note: I posted this as a community wiki, we can all add to the list, clarify, etc. Please do not judge. Keep it objective.

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Or is it just a matter of style and style guidance?

, , , , , .

1:

function square(n) {
   return n * n;
}

• ( ).
• ES2015 (ES6), ; ES2015 + , .
• square = ... ( ).
• square.prototype, .
• (, , ), .
• this, , , "" .

2:

var square = function(n) {
  return n * n;
};

• ( ), .
• ES2015, , . ES2015 + ( , , -, ES2015).
• square = ...
• square.prototype, .
• (new square) , , , , .
• (, , ), var.
• this, , , "" .

2.5: ( )

var square = function square(n) {
  return n * n;
};

2, , ES5 (square). ( , , , .)

3:

var square = (n) => {
   return n * n;
};

:

var square = n => n * n;

• ( ), .
• ( , , -, ES2015).
• square = ...
• square.prototype.
• (new square) (TypeError: square is not a constructor).
• arguments ( arguments ).
• Per spec , , this arguments. JavaScript- arguments, , this .
• (, , ), var.
• , this, this , , this ( , ).

4:

const square = (n) => {
   return n * n;
};

:

const square = n => n * n;

• , .
• ( , , -, ES2015).
• square = ...
• square.prototype.
• (new square) (TypeError: square is not a constructor).
• arguments (. 3).
• Per spec, , "" (. 3).
• ( ), ES2015 + const.
• , this, this , , this ( , ).

5: ( )

let square = (n) => {
   return n * n;
};

:

let square = n => n * n;

4, , square = ...

Answer 2

, T.J. , , . const square = n => n*n;. , , , " ES6/ES2015".

ES6- ( , , return) .