value of `this` inside of array methods

this-inside-array-methods.js

// 5 September 2023
// `this` inside array methods

// Value of `this` inside array depends on whether `this` appears in function
// vs. constructor scope, and whether the iteration method calls a normal vs. an
// arrow function.

/*
  scope       |  iterator
  ------------+------------
  function    |  function
  constructor |  function
  function    |  arrow
  constructor |  arrow
 */

/* test it out */


~(function () {
  // "use strict";

  function X(...a) {
    var t = this;

    a.slice().forEach(function (v, i, a) {
      console.info(t === self ? 'function' : 'constructor', "|", "function");
      console.log(v);
      console.log(this.constructor.name, t.constructor.name);
    });
  };

  function Y(...a) {
    var t = this;

    a.slice().forEach((v, i, a) => {
      console.info(t === self ? 'function' : 'constructor', "|", "arrow");
      console.log(v);
      console.log(this.constructor.name, t.constructor.name);
    });
  };


  X(1);
  // function |  function
  // 1
  // Window Window


  new X(2);
  // constructor |  function
  // 2
  // Window X


  Y(4);
  //  function    |  arrow
  // 4
  // Window Window


  new Y(8);
  //  constructor |  arrow
  // 8
  // Y Y
})();