CODEWITHSUNDEEP
javascript
Nicholas Rotondo
Nicholas Rotondo

Reputation: 55

proper function calling etiquette?

I may be wording this title wrong but in javascript is it ok to call a nested function like so, if not why and what are some safer or more proper ways

function foo() {
return function poo() {
console.log("ew");
}
}

var fooPoo = foo()();

Upvotes: 0

Views: 168

Answers (2)

T.J. Crowder
T.J. Crowder

Reputation: 1075587

Yes, that's fine, and fairly normal, if you want poo to have access to information that's private within foo and you don't want the calling code to have access to that information. Or even just if foo is what knows how to create the poo function, even if private information isn't needed.

It's relatively rare to do it all in one expression, because usually when you return a function from another function, you want to keep the function around:

var p = foo();
var fp1 = p();
var fp2 = p();

...but only relatively unusual, not unusual.

Here's an example of using the private information held by the context of the original call to the function (allocator, here, is like your foo):

function allocator(seed) {
    return function() {
        return seed++;
    };
}

var a = allocator(1);
console.log(a()); // 1
console.log(a()); // 2
console.log(a()); // 3

Note that the code calling a can't manipulate seed directly. It can only call a and use the value it returns.

Upvotes: 1

synthet1c
synthet1c

Reputation: 6282

Yes, it as a functional technique referred to as currying. it allows you to set parameters for the function in different places in your code

function foo(param1) {
  return function poo(param2) {
    console.log(param1, param2);
  }
}

var fooPoo = foo('param1')('param2');

A common thing I do is use currying for passing in settings when running event listeners to allow greater reuse of functions

function setColor(color) {
  return function (e) {
    e.target.background = color
  }
}

someElement.addEventLister('click', setColor('red'))

Here you can pass in your configuration when declaring your event listener but it won't be called until later when the event is fired and due to the closure you will have access to the color variable within the event listener callback. But now that I know the technique I use it quite a bit

Upvotes: 0

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