Lady’s Gitweb - Pisces/blob - function.js

   1 // ♓🌟 Piscēs ∷ function.js
   2 // ====================================================================
   3 //
   4 // Copyright © 2022‐2023 Lady [@ Lady’s Computer].
   5 //
   6 // This Source Code Form is subject to the terms of the Mozilla Public
   7 // License, v. 2.0. If a copy of the MPL was not distributed with this
   8 // file, You can obtain one at <https://mozilla.org/MPL/2.0/>.
   9
  10 import { ITERATOR } from "./value.js";
  11
  12 export const {
  13   /**
  14    * Creates a bound function from the provided function using the
  15    * provided this value and arguments list.
  16    *
  17    * ☡ As with call and construct, the arguments must be passed as an
  18    * array.
  19    */
  20   bind,
  21
  22   /**
  23    * Returns a new function which calls the provided function with its
  24    * first argument as the `this` value and the remaining arguments
  25    * passed through.
  26    *
  27    * ※ This is effectively an alias for Function.prototype.call.bind.
  28    */
  29   makeCallable,
  30 } = (() => {
  31   // ☡ Because these functions are used to initialize module constants,
  32   // they can’t depend on imports from elsewhere.
  33   const {
  34     bind: functionBind,
  35     call: functionCall,
  36   } = Function.prototype;
  37   const callBind = Reflect.apply(functionBind, functionCall, [
  38     functionBind,
  39   ]);
  40   const {
  41     create: objectCreate,
  42     defineProperty: defineOwnProperty,
  43     getPrototypeOf: getPrototype,
  44   } = Object;
  45   const { [ITERATOR]: arrayIterator } = Array.prototype;
  46   const {
  47     next: arrayIteratorNext,
  48   } = getPrototype([][ITERATOR]());
  49   const argumentIterablePrototype = {
  50     [ITERATOR]() {
  51       return {
  52         next: callBind(
  53           arrayIteratorNext,
  54           call(arrayIterator, this.args, []),
  55         ),
  56       };
  57     },
  58   };
  59   return {
  60     bind: ($, boundThis, boundArgs) =>
  61       callBind(
  62         $,
  63         boundThis,
  64         ...objectCreate(
  65           argumentIterablePrototype,
  66           { args: { value: boundArgs } },
  67         ),
  68       ),
  69     makeCallable: ($) =>
  70       defineOwnProperty(
  71         callBind(functionCall, $),
  72         "length",
  73         { value: $.length + 1 },
  74       ),
  75   };
  76 })();
  77
  78 /**
  79  * Calls the provided function with the provided this value and
  80  * arguments list.
  81  *
  82  * ☡ This is an alias for Reflect.apply—the arguments must be passed
  83  * as an array.
  84  */
  85 export const call = Reflect.apply;
  86
  87 /**
  88  * Constructs the provided function with the provided arguments list
  89  * and new target.
  90  *
  91  * ☡ This is an alias for Reflect.construct—the arguments must be
  92  * passed as an array.
  93  */
  94 export const construct = Reflect.construct;
  95
  96 /**
  97  * Returns the provided value.
  98  *
  99  * ※ This function can be called as a constructor. When used in an
 100  * `extends` clause and called via `super`, it will set the value of
 101  * `this` to the provided value, enabling it to be extended with
 102  * private class features.
 103  */
 104 export const identity = function ($) {
 105   return $;
 106 };
 107
 108 /** Returns whether the provided value is callable. */
 109 export const isCallable = ($) => typeof $ === "function";
 110
 111 /** Returns whether the provided value is a constructor. */
 112 export const isConstructor = ($) => {
 113   // The provided value is an object.
 114   try {
 115     construct(
 116       function () {},
 117       [],
 118       $,
 119     ); // will throw if $ is not a constructor
 120     return true;
 121   } catch {
 122     return false;
 123   }
 124 };
 125
 126 /**
 127  * Returns whether the provided object inherits from the prototype of
 128  * the provided function.
 129  */
 130 export const ordinaryHasInstance = makeCallable(
 131   Function.prototype[Symbol.hasInstance],
 132 );