Description

The JavaScript String method toLowerCase() returns the given string in lowercase, without changing the original string.

  • It returns a new string and doesn't change the original string.
  • It is commonly used to convert a text to its lowercase.

Syntax

The method toLowerCase() has the below syntax, where str is a string.

str.toLowerCase()

Parameters

The method toLowerCase() doesn't allow any parameters.

Result

Returns the lowercase representation of a string, without changing the original string.

Returns TypeError for null and undefined values.

Example 1: Using the Method

The below example shows the basic usage of the method.

var str1 = "Hello World!";
var str2 = "HELLO WORLD!";
var str3 = "hello world!";

document.write(str1.toLowerCase());    // Prints: hello world!
document.write(str2.toLowerCase());    // Prints: hello world!
document.write(str3.toLowerCase());    // Prints: hello world!

Output:

hello world!
hello world!
hello world!

Example 2: Method Returns TypeError

The method returns TypeError for null and undefined values.

var str1;           // This variable contains undefined
var str2 = null;    // This variable contains null

// Returns TypeError
document.write(str1.toLowerCase());    // Returns TypeError
document.write(str2.toLowerCase());    // Returns TypeError

Output:

TypeError: Cannot read properties of undefined (reading 'toLowerCase')
TypeError: Cannot read properties of null (reading 'toLowerCase')

Overall

The JavaScript String method toLowerCase() returns the given string in lowercase, without changing the original string.

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