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Point-free gotchas in JavaScript

Dan Homola on February 26, 2018

Note: this post was originally published on my Medium profile I am a big fan of functional programming, I enjoy the conciseness of it and it fits ...
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Ozan Seymen •

Thanks for the article Dan!

I believe the solution to your first gotcha is "unary" (e.g. ramdajs.com/docs/#unary) - something like:

const R = require('ramda')

const nums = ["25", "45", "11"]
console.log(nums.map(R.unary(Number.parseInt)))
// logs [ 25, 45, 11 ]

I am a little confused with how your second gotcha (this losing context) is related specifically to the pointfree style. I thought this is a general issue with this and not specifically tied to pointfree. Your first example in the second gotcha also suggests that (no pointfree there). Am I missing something?

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Dan Homola •

Thanks for the comment! The unary function seems neat, I will definitely give Ramda a closer look :)

As for the second gotcha it is simply to illustrate that () => foo() cannot always be replaced by foo as a more "point-free" style. I hope it is clearer now.

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Tom Clift •

In your bind example, it might be worth mentioning a related gotcha: bind sends arguments as additional parameters. In your getMessage example, if getMessage took a number, and you bound from a function with an unrelated number param, you get a nasty surprise!

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Dan Homola •

Thanks for the addition, I did not realise that!

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Bauke Regnerus •

Thanks for this well written article. It describes exactly the reason why I prefer closures over point-free functions. The short notation of point-free looks great, but the lack of control over the scope as well as the arguments passed in has caused many flaws in my Javascript code over the years.

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Dan Homola •

Thank you for your kind comment, I'm glad you liked it :)

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Andy Coates •

'Fix B' from above could be expressed slightly more elegantly as:

// Fix B - binding
const isActivationCodePointFree = RegExp.prototype.test.bind(/^\d{4}-\d{4}-\d{4}$/);