Listening for variable changes in JavaScript

Question

Is it possible to have an event in JS that fires when the value of a certain variable changes? JQuery is accepted.

Answer 1

Using Prototype: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/defineProperty

// Console
function print(t) {
  var c = document.getElementById('console');
  c.innerHTML = c.innerHTML + '
' + t;
}

// Demo
var myVar = 123;

Object.defineProperty(this, 'varWatch', {
  get: function () { return myVar; },
  set: function (v) {
    myVar = v;
    print('Value changed! New value: ' + v);
  }
});

print(varWatch);
varWatch = 456;
print(varWatch);

Other example

// Console
function print(t) {
  var c = document.getElementById('console');
  c.innerHTML = c.innerHTML + '
' + t;
}

// Demo
var varw = (function (context) {
  return function (varName, varValue) {
    var value = varValue;
  
    Object.defineProperty(context, varName, {
      get: function () { return value; },
      set: function (v) {
        value = v;
        print('Value changed! New value: ' + value);
      }
    });
  };
})(window);

varw('varWatch'); // Declare
print(varWatch);
varWatch = 456;
print(varWatch);

print('---');

varw('otherVarWatch', 123); // Declare with initial value
print(otherVarWatch);
otherVarWatch = 789;
print(otherVarWatch);