difference on javascript constructors

Question

Is there any difference between these 2 apart from the resolving constructor?

var Person = function(living, age, gender) {
    this.living = living;
    this.age = age;
    this.gender = gender;
    this.getGender = function() {
        return this.gender;
    };
};

var Person = function Person(living, age, gender) {
    this.living = living;
    this.age = age;
    this.gender = gender;
    this.getGender = function() {
        return this.gender;
    };
};

Both could be invoked using

var p = new Person("Yes",25,"Male");

The first one resolves to function() where the latter resolves to person(), but I would like to know if there is any advantage of using one over the other

Somewhat related: stackoverflow.com/questions/336859/…

James Donnelly
– James Donnelly

2013-05-21 22:28:32 +00:00
Commented May 21, 2013 at 22:28 — James Donnelly
– James Donnelly, Commented May 21, 2013 at 22:28
Further reading: kangax.github.io/nfe

user123444555621
– user123444555621

2013-05-22 00:01:04 +00:00
Commented May 22, 2013 at 0:01 — user123444555621
– user123444555621, Commented May 22, 2013 at 0:01

Benjamin Gruenbaum · Accepted Answer · 2013-05-21 22:31:03Z

6

They are identical for the purposes you speak of.

The only difference that inside the second function you have a clean reference to the function from within itself.

Formally

The language specification states:

FunctionExpression :

function Identifier(opt) ( FormalParameterListopt ) { FunctionBody }

The identifier (in this case Person) in the function expression is optional

The reasoning for that is explained a bit later in the language specification:

NOTE The Identifier in a FunctionExpression can be referenced from inside the FunctionExpression's FunctionBody to allow the function to call itself recursively. However, unlike in a FunctionDeclaration, the Identifier in a FunctionExpression cannot be referenced from and does not affect the scope enclosing the FunctionExpression.

In practice

You can use the second option in two situations:

When it makes your code more understandable:

   (function removeBodyDivs(){
        //does logic removing
        //divs from the body
   })();

Can be more understandable than:

   (function (){
        //does logic removing
        //divs from the body
   })();

When doing recursion, for example

  var f = function fib(n){
      return n<2?2:(fib(n-1)+fib(n-2));
  }

edited May 21, 2013 at 22:31

answered May 21, 2013 at 22:25

Benjamin Gruenbaum

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13 Comments

Ian Over a year ago

But how does this relate to a constructor? For a normal function, that makes sense. But for a constructor, I can't see it having any effect. You never call the constructor from within

Benjamin Gruenbaum Over a year ago

@Ian Good question, just because you should't do something doesn't mean people don't do it. You can, for example return an object from a constructor function which would make the new 99.9% meaningless. jsfiddle.net/NuT5F . I did start with "They are identical for the purposes you speak of."

zerkms Over a year ago

@Ian: "You never call the constructor from within" --- imagine a tree-like structure. Some particular node of a particular type may create a nested node of the same type by default.

zerkms Over a year ago

@Benjamin Gruenbaum: yep, for objects it makes sense.

mrówa Over a year ago

Additional point: Having named constructor might be useful in debugging.

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