Is Javascript a Functional Programming Language?

Question

Just because functions are first class objects, there are closures, and higher order functions, does Javascript deserve to be called a Functional Programming language? The

Answer 1

As we know the functional programming language doesn't allow to change or mutate the elements(state)of functions but in javascript it is allowed in that sense it is not a functional programming language, although it does treat function as first class citizens.

Answer 2

I tend not to think of programming languages as having one particular paradigm, but that they lend themselves to certain paradigms. However just because they lend themselves to a particular paradigm doesn't mean you have to use that paradigm. It's quite possible to write object oriented programs in C and write imperative programs in ML. Not using a certain paradigm to solve a problem because the language isn't designed for it is just artificially limiting yourself (of course you should still take into account the limitations of a language when deciding if a particular solution will be a good solution).

Answer 3

In Javascript, you can do something like this!!

// Data
var fruits = [
    { name: 'apple',  price: 5 }, 
    { name: 'orange', price: 10 }, 
    { name: 'lemon',  price: 15 }
]

// Request Data from magicURL
request('magicURL')
    .then(selectKeyOf('price'))
    .then(priceMethod('sum'))
    .then((result)=>{
        console.log(result) // 30
    })

I have made a github page in order to demo this concept and you can clone/view my implementation

Answer 4

Repeating my own answer to a similar question,

There's no accepted definition of functional programming language.

If you define functional language as the language that supports first class functions and lambdas, then yes, JavaScript *is* a functional language.

If you also consider the factors like support for immutability, algebraic data types, pattern matching, partial application etc then no, JavaScript *is not* a functional language.

---

I'd encourage you to read the following related blog posts (and also the comments below them):

• Scala is not a functional language

• Erlang is not functional

• Reddit discussion on "Erlang is not functional"

Answer 5

Well, I wouldn't say it's functional programming, but then I would say it's object oriented and just today a friend said he wouldn't put it on that shelf either.

So, while I wouldn't say it is, I guess there's room for opinion. It does have classical features of functional programming, it doesn't have others.

Answer 6

@petraszd I rewrite your code a little to obtain a "new" for operator:

   
   function ffor(a, b, f){
     function it(i){
       if(i > b)return
       f(i)
       it(i+1)
     }
     it(a)
   }

   print("----" + new Date()+"----")

   var funcs = []
   ffor(0, 9, function(i){
     funcs.push(function(){return i})
   })

   ffor(0, 9, function(i){
     print(funcs[i]())
   })

But I know that this way has disadvantages for big loops...

Related question about tail recurtion optimization in JS

P.S. Posted here cuz have problem with code formatting while posting as comment