Deprecated: This feature is no longer recommended. Though some browsers might still support it, it may have already been removed from the relevant web standards, may be in the process of being dropped, or may only be kept for compatibility purposes. Avoid using it, and update existing code if possible; see the compatibility table at the bottom of this page to guide your decision. Be aware that this feature may cease to work at any time.

The toSource() method returns a string representing the source code of the object.



Return value

A string representing the source code of the object.


The toSource() method returns the following values:

  • For the built-in Object object, toSource() returns the following string indicating that the source code is not available:
      function Object() {
          [native code]
  • For instances of Object, toSource() returns a string representing the source code.

You can call toSource() while debugging to examine the contents of an object.

Overriding the toSource() method

It is safe for objects to override the toSource() method. For example:

function Person(name) {
  this.name = name;

Person.prototype.toSource = function Person_toSource() {
  return 'new Person(' + uneval(this.name) + ')';

console.log(new Person('Joe').toSource()); // ---> new Person("Joe")

Built-in toSource() methods

Each core JavaScript type has its own toSource() method. These objects are:

Limitations on cyclical objects

In the case of objects that contain references to themselves, e.g. a cyclically linked list or a tree that can be traversed both ways, toSource() will not recreate the self-reference, as of Firefox 24. For example:

const obj1 = {};
const obj2 = { a: obj1 };
obj1.b = obj2;

console.log('Cyclical: ' + (obj1.b.a == obj1));

const objSource = obj1.toSource(); // returns "({b:{a:{}}})"

obj1 = eval(objSource);

console.log('Cyclical: ' + (obj1.b.a == obj1));

If a cyclical structure is employed and toSource() is needed, the object must provide an override to toSource(), either using a reference to a constructor or providing an anonymous function.


Using toSource()

The following code defines the Dog object type and creates theDog, an object of type Dog:

function Dog(name, breed, color, sex) {
  this.name = name;
  this.breed = breed;
  this.color = color;
  this.sex = sex;

theDog = new Dog('Gabby', 'Lab', 'chocolate', 'female');

Calling the toSource() method of theDog displays the JavaScript source that defines the object:

// returns ({name:"Gabby", breed:"Lab", color:"chocolate", sex:"female"})


Not part of any standard.

Browser compatibility

BCD tables only load in the browser

See also