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xtuc/compose.js Secret

Created July 3, 2017 11:14
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// compose function
String.prototype.ᐅ = function(f) {
return f(this)
}
function doubleSay (str) {
return str + ", " + str;
}
function capitalize (str) {
return str[0].toUpperCase() + str.substring(1);
}
function exclaim (str) {
return str + '!';
}
let result = "hello"
.ᐅ (doubleSay)
.ᐅ (capitalize)
.ᐅ (exclaim)
result //=> "Hello, hello!"
@pi0
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pi0 commented Jul 3, 2017

@steida But neither is working for string!

Object.defineProperty(Object, '$$', {get: function (f) { return f(this) }})
Object.defineProperty(Object, '$$', function (f) { return f(this) })

@xtuc
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Author

xtuc commented Jul 3, 2017

I prefer the symbol because it's look like the |> symbol used in most functional programming languages. But it's not a valid identifier in JavaScript.

@rickmed
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rickmed commented Jul 3, 2017

Function.prototype. = function(f) {
  const self = this
  return function(...args) {
    return f(self(...args))
  }
}

const doubleSay = str => str + ", " + str
const capitalize = str => str[0].toUpperCase() + str.substring(1)
const exclaim = str => str + '!'

const program =
  doubleSay
  . (capitalize)
  . (exclaim)

program('hello')  //=> "Hello, hello!"

@katemihalikova
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// compose function
const ƒ = (_, ...inputs) => inputs.reduce((res, fn) => fn(res))

const doubleSay = str => str + ", " + str
const capitalize = str => str[0].toUpperCase() + str.substring(1)
const exclaim = n => str => str + '!'.repeat(n)

let input = "hello"

let result = ƒ `
${input}
  |> ${doubleSay}
  |> ${capitalize}
  |> ${exclaim(3)}
`

result //=> "Hello, hello!!!"

@kapouer
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kapouer commented Jul 4, 2017

I'd use ø because it's not used, and available in english and french.
Also it reminds of the mathematical composition operator (which is just o).

@xaviervia
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@rickmed has a point here :D

@morkro
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morkro commented Jul 4, 2017

@rickmed we could also add some arrow functions to get rid of the const self = this. Although it might be less readable.

Function.prototype. = function(f) {
  return (...args) => f(this(...args))
}

const doubleSay = str => str + ", " + str
const capitalize = str => str[0].toUpperCase() + str.substring(1)
const exclaim = str => str + '!'

const program =
  doubleSay
  . (capitalize)
  . (exclaim)

program('hello')  //=> "Hello, hello!"

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