tests that an argument is the scope or that a value is the scope's value

is-this.js

// 10 April 2018
// Tuesday fun with this and that
// Object.prototype.isThis(argument) tests whether an argument is the scope or a value is the scope's value

Object.prototype.isThis = function isThis(o) {
  return o == null ? isThis.call(o, this) : o === this.valueOf();
}

console.log(
  // true
  'a'.isThis('a'),
  (0).isThis(0),
  (false).isThis(false),
  Object.isThis(Object),
  window.isThis(window),
  window.isThis(),
  this.isThis(this),
  this.isThis(),
  
  // assignment
  (function() { 
    var a = { 'test': 'test'};
    var b = a;
    return a.isThis(b)
  })(),
  
  // constructors
  (function() {
    function A(name) { this.name = name || 'defaultName'; }
    var name = 'test'
    var a = new A(name);
    var b = new A(name);
    return a.isThis(a) && (a.name).isThis(name) && (b.name).isThis(a.name);
  })(),
  
  // context: weakness in the 'context' or 'scope' mechanism
  // where scope is null, it is set to outer scope, etc...
  {}.isThis.call(undefined, null)
);
// true true true true true true true true true true true

console.log(
  // false
  ('').isThis(' '),
  (0).isThis(false),
  (1).isThis(true),
  (1).isThis('1'),
  ({}).isThis({}),
  ([0]).isThis([0]),
  
  // constructors
  (function() {
    function A() {}
    var a = new A();
    var b = new A();
    return b.isThis(a);
  })(),
  
  // context
  {}.isThis.call({}, null),
);
// false false false false false false false false