JavaScript toLowerCase(): Convert a String to Lowercase

The JavaScript toLowerCase() method converts a specified string to lowercase. For example:

HTML with JavaScript Code

<!DOCTYPE html>
<html>
<body>

   <p id="xyz"></p>

   <script>
      let myString = "JavaScript is Fun. Is not it?";

      let myLowerString = myString.toLowerCase();
      document.getElementById("xyz").innerHTML = myLowerString;
   </script>
   
</body>
</html>

Output

In the above example, the first statement or the code declares a variable myString and assigns it a string value, "JavaScript is Fun. Is not it?".

Then, the toLowerCase() function is called on the myString variable to convert all the characters to lowercase. The result is stored in the myLowerString variable.

Finally, the code sets the innerHTML property of an HTML element with the ID of xyz to the value of myLowerString, which will display the converted string in all lowercase letters in the HTML page.

That is, all the uppercase characters of the specified string will be converted into their lowercase equivalent.

JavaScript toLowerCase() syntax

The syntax of the toLowerCase() method in JavaScript is:

string.toLowerCase()

The toLowerCase() method does not change the original string. Rather, it returns a new string that is an exact copy of the original string, except that all characters will be in lowercase.

Advantages of the toLowerCase() function in JavaScript

When searching for a specific string, it is often helpful to convert the input string and the search term to lowercase first, so that the search is case-insensitive. For this purpose, the toLowerCase() function makes it simple to convert a string to lowercase.
The toLowerCase() function is useful for normalizing strings, particularly for comparison or sorting. Because different letters have different Unicode code points, two visually identical strings can have different binary representations. The toLowerCase() function ensures that strings, regardless of their original form, are normalized to lowercase according to the Unicode standard.
When working with user inputs or displaying data, the toLowerCase() function can be used to ensure that strings are consistently formatted in a consistent case style.

Disadvantages of the toLowerCase() function in JavaScript

Depending on the language and locale of the input string, the toLowerCase() function's behavior may change. For instance, some languages have letters that cannot be made lowercase and others have different capitalization conventions. As a result, not all languages and locales will always see the results that are expected from the function.
It might not be possible to restore the characters' original cases since the toLowerCase() function converts all characters to lowercase. This can be a problem when working with proper nouns or when producing output that needs to be capitalized, for example, when the original case is required for some reason.
Performance issues may arise if the toLowerCase() function is applied to large strings or used repeatedly in a loop. By allocating memory and copying the contents of the original string, the function creates a new string, which can be a laborious process.

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