Using setters and getters to find what changed a property

Let’s say you have an object like this:

var myObject = {
    name: 'Peter'
}

Later in your code, you try to access myObject.name and you get George instead of Peter. You start wondering who changed it and where exactly it was changed. There is a way to place a debugger (or something else) on every set (every time someone does myObject.name = 'something'):

var myObject = {
    _name: 'Peter',
    set name(name){debugger;this._name=name},
    get name(){return this._name}
}

Note that we renamed name to _name and we are going to define a setter and a getter for name.

set name is the setter. That is a sweet spot where you can place debugger, console.trace(), or anything else you need for debugging. The setter will set the value for name in _name. The getter (the get name part) will read the value from there. Now we have a fully functional object with debugging functionality.

Most of the time, though, the object that gets changed is not under our control. Fortunately, we can define setters and getters on existing objects to debug them.

// First, save the name to _name, because we are going to use name for setter/getter
otherObject._name = otherObject.name;

// Create setter and getter
Object.defineProperty(otherObject, "name", {
    set: function(name) {debugger;this._name = name},
    get: function() {return this._name}
});

Check out setters and getters at MDN for more information.

Browser support for setters/getters:

|———|––––|———|––|—––|––––|––––| | Version | 1 | 2.0 | 9 | 9.5 | 3 | all |

Found a mistake? Have a question or improvement idea? Let me know.

Debugging:

* Interactive interpreter variables

* Breakpoints

* Using setters and getters to find what changed a property

* Using the console

* Including a stack trace when logging - console.trace

* Automatically pausing execution

* Tabulating values - console.table

* Elements inspector

* Stepping through code

* Break when a function is called

Table Of Contents

0 Getting started

1 Comments

2 Basic data types

3 Built-in constants

4 Variables

5 Declarations and assignments

6 Reserved keywords

7 Data types in JavaScript

8 Strings

9 Escape sequences

10 Template Literals

11 Arrays

12 Objects

13 Prototypes objects

14 Classes

15 Variable coercion / conversion

16 Map

17 Set

18 Arithmetic Math

19 Bitwise operators

20 Bitwise operators

21 Unary Operators

22 Comparison operations

23 Conditions

24 Loops

25 Functions

26 Arrow functions

27 Date

28 Date comparison

29 Scope

30 AJAX

31 Promises

32 Regular Expression

33 Error Handling

34 Geolocation

35 Cookies

36 Intervals and timeouts

37 Generators

38 History of visited urls

39 Strict mode

40 Custom Elements

41 JSON

42 Binary Data

43 Web Storage

44 Fetch

45 Modules

46 Screen

47 Inheritance

48 Timestamps

49 Destructuring assignment

50 Web Worker

51 Debugging

52 Notifications API

53 WebSockets

54 Web Cryptography API

55 Async functions, async / await

56 Constructor functions

57 execCommand and contenteditable

58 Performance Tips

59 Design patterns

60 requestAnimationFrame

61 Method chaining

62 Global error handling in browsers

63 File API, blobs and FileReaders

64 Console

65 Tail call optimization

66 Detecting browser

67 Enumerations

68 Symbols

69 Localization

70 Selection API

71 Callbacks

72 Functional JavaScript

73 Modals

74 Data attributes

75 Event Loop

76 Events

77 Data manipulation

78 BOM Browser Object Model

79 Unit Testing

80 Linters for ensuring code quality

81 Automatic Semicolon Insertion

82 IndexedDB

83 Anti-patterns

84 Navigator Object

85 Modularization techniques

86 Proxy

87 Same origin policy, cross-origin communication

88 postMessage and MessageEvent

89 WeakMap

90 WeakSet

91 Behaviroal Design Patterns

92 Server-sent events

93 Async iterators

94 Namespacing

95 Evaluating JavaScript

96 Memory efficiency

97 How to make iterator usable inside async callback function

98 Context this

99 Setters and getters

100 Vibration API

101 Fluent API

102 Tilde

103 Security issues

104 Get and set CSS custom variables

105 Contributors