JavaScript Object.prototype.toString() Method

In JavaScript, the  Object.prototype.toString() method is used to return a string that can represent the object. The toString() method is automatically inherited by every object which is inherited from Object.  Whenever an object is represented as a text value or a string is expected from the object, the toString() method is called automatically.  

Syntax:

obj.toString()

If one does not override the toString() method in case of custom objects, the toString() method returns the following:

[object type] 

In the above syntax, the type denotes the object type.

Another use of the toString() method is that it can be used to convert base 10 numbers (and even bigInts) to other base numbers. 

Syntax:

ExNum.toString(radix);

In the above syntax, the ExNum is an object of the object type number or bigInt and the radix refers to the base the number to is be converted to.

Example 1: The following example shows how the toString() method works when dealing with default object type and custom object type when the toString() method is not overridden.

JavaScript

// Creating a custom object type
function ExObjType(n) {
    this.number = n;
}

function myFunction() {
    // Creating an object of the
    // String class
    const o = new String('Hello');
    console.log(o.toString());

    // Creating an object ExObj1 of
    // custom defined class
    const ExObj1 = new ExObjType(3);

    // Returns [object Object] as toString()
    // not overridden for custom class
    console.log(ExObj1.toString());
}
myFunction();

Output:

Hello
[object Object]

Example 2: The following example shows how the toString() method works when dealing with custom object type and the toString() method is overridden  :

JavaScript

// Creating a custom object type
function ExObjType(n) {
    this.number = n;
}

// Overriding the toString() method
// for ExObjectType
ExObjType.prototype.toString = function ExObjToString() {
    const ans = 'The number related to this object is '
    + this.number;
    return ans;
}

function myFunction() {
    // Creating an object ExObj1 of
    // custom defined class
    const ExObj1 = new ExObjType(3);

    // Calling the toString() method
    // after overriding
    console.log(ExObj1.toString());
}
myFunction();

Output:

The number related to this object is 3

Example 3: The following example shows how to use the toString() method to convert base 10 numbers to different base numbers.

JavaScript

function myFunction() {
    // Creating a constant num1
    // with value 12
    const num1 = 12;

    // Converts num1 to a binary form
    console.log(num1.toString(2));

    // Converts num1 to its octal form
    console.log(num1.toString(8));

    // Converts num1 to its base-5 form
    console.log(num1.toString(5));
}
myFunction();

Output:

1100
14
22

We have a complete list of Javascript Object methods, to check those please go through this Objects in Javascript article.

We have a Cheat Sheet on Javascript where we covered all the important topics of Javascript to check those please go through Javascript Cheat Sheet-A Basic guide to JavaScript.