I have found a script example, in it there is a line of code that looks something like this:

fn = (arg1) => (arg2) => {
    //do something with arg1 and arg2
}

I am wondering exactly what is happening here, and how would it look as a "normal" function?

I have found a script example, in it there is a line of code that looks something like this:

fn = (arg1) => (arg2) => {
    //do something with arg1 and arg2
}

I am wondering exactly what is happening here, and how would it look as a "normal" function?

• javascript
• ecmascript-6

• related: What do multiple arrow functions mean in javascript? – user6445533 Commented Mar 27, 2017 at 13:31

3 Answers 3

fn = (arg1) => (arg2) => {
    //do something with arg1 and arg2
}

fn is a name for the first anon function its basically a function that returns another function

it translated roughly to

var fn = function(arg1){
  return function(arg2){
    ... // do something 
  }
}

noting that the this value will differ because it is an arrow function .

It looks like two nested function, where the outer function returns the inner function with a closure over arg1.

var fn = function (arg1) {
        return function (arg2) {
            //do something with arg1 and arg2
        };
    };

var fn = function (arg1) {
        return function (arg2) {
            return arg1 + arg2;
        };
    };


var add4 = fn(4),
    add20 = fn(20);

console.log(add4(5));  //  9
console.log(add20(5)); // 25

Arrow function:

An arrow function expression has a shorter syntax than a function expression and does not bind its own this, arguments, super, or new.target. These function expressions are best suited for non-method functions, and they cannot be used as constructors.

I cannot add ments so I write this as an answer. Your example is also known as currying a concept that allows you to pass in a subset of arguments to a function and get a function back that’s waiting for the rest of the arguments.