toString() on an object

JavaScriptMiddle~1 min read

The toString() method is JavaScript's built-in way to convert an object into a string (string representation).

This method is called automatically, when an object needs to be used in a text context - for example, during concatenation (+), logging, template strings, and so on.

Short version

Syntax:

javascript

obj.toString()

Returns the string representation of the object.

Example - basic behavior

javascript

const user = { name: 'Alice' };

console.log(user.toString()); // "[object Object]"

By default toString() is inherited from Object.prototype, and returns a string of the form:

javascript

"[object ObjectType]"

When it is called automatically

javascript

const user = { name: 'Alice' };

console.log('User: ' + user);
// "User: [object Object]"

alert(user);
// "[object Object]"

JS automatically calls toString() to turn the object into a string.

You can override `toString()`

You can set your own string representation of the object:

javascript

const user = {
  name: 'Alice',
  age: 25,
  toString() {
    return `${this.name} (${this.age})`;
  }
};

console.log(String(user));     // "Alice (25)"
console.log('User: ' + user); // "User: Alice (25)"

During + concatenation or String(obj) - the overridden toString() is called.

Comparison with `valueOf()`

When JS tries to convert an object to a primitive, it calls, in priority order:

obj[Symbol.toPrimitive] (if present)
obj.toString() (if a string is expected)
obj.valueOf() (if a number is expected)

Example:

javascript

const user = {
  name: 'Alice',
  valueOf() {
    return 42;
  },
  toString() {
    return 'User';
  }
};

console.log(String(user)); // "User"
console.log(Number(user)); // 42

Different built-in objects have their own `toString()`

Type	Example	Result
`Object`	`{}`	`[object Object]`
`Array`	`[1, 2, 3].toString()`	`"1,2,3"`
`Date`	`(new Date()).toString()`	`"Tue Oct 14 2025 17:00:00 GMT+0300 (...)"`
`Function`	`(() => {}).toString()`	`"() => {}"`
`RegExp`	`/abc/.toString()`	`"/abc/"`
`Map`, `Set`	`[object Map]`, `[object Set]`	not revealed

Advanced example - formatting JSON

If you want a string with the object's contents, not just [object Object], use JSON.stringify():

javascript

const user = { name: 'Alice', age: 25 };
console.log(user.toString());          // "[object Object]"
console.log(JSON.stringify(user));     // '{"name":"Alice","age":25}'

JSON.stringify() is not toString(), it is a separate JSON serialization mechanism.

SUMMARY

What it does	Converts an object into a string
Where it's defined	`Object.prototype.toString`
By default	Returns `"[object Object]"`
Can be overridden	Yes
Called automatically	during concatenation, `String()`, logs, template strings
Alternative	`JSON.stringify(obj)` - for full contents

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