Currently, I am utilizing a third-party library that utilizes a function with functions as arguments. During my conditional checks, I determine whether to add a particular function as a parameter or not. However, providing null in these cases results in errors.
I came across this code snippet that seems to solve the issue, but the functionality is still unclear to me:
compose(__DEV__ ? devTools() : f => f)
Would f => f be similar to () => {}, being an empty anonymous function?
The identity function, denoted as f => f, simply returns the argument that it receives.
Commonly used as a default value in transformation processes, this function does not alter or transform its input in any way.
Is the identity function
f => fthe same as an empty anonymous function() => {}?
No, they are not equivalent. The empty function does not return any value, while the identity function returns the original argument provided to it.
Function x => x is almost identical to function(x){ return x; }
Close, but not an exact match.
* - While there are some subtle differences pointed out in the comments, they may not be crucial for this specific question. However, they can be significant in different contexts.
If you're curious about the meaning of f => f, remember that the left side represents the parameter while the right side indicates the return value. For instance, if you see f => f*2, it can be rewritten as:
function(f) {
return f * 2;
}
This specific code snippet simply returns whatever input is given to it.
https://developer.mozilla.org/en/docs/Web/JavaScript/Reference/Functions/Arrow_functions
I won't delve into the details of what f => f does since it has already been discussed by others. Instead, I will focus on explaining the remaining part of the function as there is a distinction between f => f and __DEV__ ? devTools() : f => f
The conditional operator evaluates whether __DEV__ holds a truthy value. If true, it returns the devTools() function. If false, it returns the identity function f => f, which essentially performs no action. In other words, this segment of code activates certain functions specific to development mode. The exact functionalities that are enabled remain ambiguous without further context, but presumably, they involve additional logging details and reduced obfuscation.
If you ever find yourself in a similar situation, Babel can help provide the solution. Simply visit Babel to get the answer.
Here is what it outputted:
"use strict";
(function (f) {
return f;
});
By the way, the => symbol used is an ES6 feature known as arrow expression. Another interesting expression is:
() => {}; // es6
This would be converted to:
(function () {});
Since arrow function expressions are always anonymous, consider adding a name to the function like this:
let empty = () => {}; // es6
This would then convert to:
var empty = function empty() {};
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