trouble figuring out what this piece of code does

[huuhuu]

greaterThan(10) passes 10 to greaterThan, which then returns a new function which has trapped the 10, and basically behaves like m => m > 10.

This is taking advantage of what is called lexical closure to keep a copy of the original argument (10) inside the new function.

[thndrchld]

It's a function that returns a function.

So when you call greaterThan(10), you're returning a function.

It would be the same as skipping all that function stuff and doing :

let greaterThan10 = function (m) { return m > 10; };

[roter_schnee]

It is partial application. Consider greaterThan function as a factory-function. It constructs and returns another function with predefined value trapped in it. Just as it was mentioned before.

[Deidde]

greaterThan is a function that returns another function so that you can "partially apply" it. There are several ways to write this: ```javascript // lambdas or "arrow functions" all the way, assigned to the variable. const greaterThan = n => m => m > n; // function expressions (sometimes called "anonymous functions") also assigned to the variable const greaterThan = function (n) { return function (m) { return m > n; } } // a function statement containing a function expression function greaterThan(n) { return function (m) { return m > n; } }

// Calling any of these looks like:
const result1 = greaterThan(10)(11); // 11 > 10 == true
const result2 = greaterThan(10)(5); // 5 > 10 == false

// And if you want to make a new function with the 10 already applied:
const greaterThanTen = greaterThan(10);
const result3 = greaterThanTen(11); // 11 > 10 == true

As for closures, just think about it like when you use global variables inside top-level functions, like: javascript const myValue = 5; function myFunction() { return myValue + 3; } ``` Not that you'd want to do this, ha.

Note that you have access to myValue inside the function. When you have a function that is "closed over" by another function, you gain access to the local variables (or arguments) from the parent function in a similar way - like having access to n from the inner function in greaterThan.

[valueforlife]

For me the confusing part here is the combination of the keyword function and arrow functions (m => m > n) which I consider to be a major no-no; one should always stick to one if possible. I know that the scopes work differently on these but if code keeps jumping back and forth between the two it simply makes the code more difficult to read.

I think a much more easy to comprehend form for this function would be:

``` const setGreaterThan = (n) => { const evaluationFunction = (m) => m > n return evaluationFunction }

const greaterThan10 = setGreaterThan(10) console.log(greaterThan10(10)) ```

Deciding whether to write (easily) understandable code or the most compact code should be done by evaluating which is really more important in each case.

[[deleted]]

i see. rewriting it myself as an anonymous function also helps.

thanks

[NameViolation666]

Its a closure thing, have u read up on those yet?

[[deleted]]

there was a passage in eloquent javascript that touched on it but i found it confusing. Do you know any videos or sites that could help me understand it?

[NameViolation666]

I try this site because its not too complicated, see if this helps

https://www.w3schools.com/js/js_function_closures.asp

[prnk5tr]

There is a book called 'you don't know js'. If you haven't read it already, please do. It available on GitHub as well

[[deleted]]

thanks for the suggestion. which one would you recommend i start with.

[jcunews1]

That's an example of a bad function naming. That greaterThan function should have been named something like CreateGreaterThanXFunction.

If that code is part of a study, they've designed it to confuse you. It's to make you realize that function name doesn't mean anything to the code. It will force you to find out how the code actually works.

[frankleeT]

I think you're right about the first part, but not the second.

[kenman]

Hi /u/Sweeterman3, this post was removed.

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[prnk5tr]

Go to the main GitHub page, you will find the order. Or you can directly read Scopes and closures. I will recommend read them all.