Strings are a fundamental part of working with JavaScript. And the toLowerCase() method is one of the many integrated methods that you can use to work with strings.

In this article, we'll see how to make strings lowercase with the toLowerCase() method in Python.

What is a String?

A string is a data type that can contain many different characters. A string is written as a series of characters between single or double quotes.

const exampleString = 'I am a String!'
console.log(exampleString); // I am a String!

What is a Method?

A method is a function that you can use on a specific data type. Methods can either take or not take arguments.

How Does the toLowerCase() Method Work?

The toLowerCase() method is a string method that returns a new string that's completely lowercase. If the original string has uppercase letters, in the new string these will be lowercase. Any lowercase letter, or any character that is not a letter, is not affected.

console.log(exampleString.toLowerCase()); // i am a string!

console.log('FREECODECAMP'.toLowerCase()); // freecodecamp

What to Keep in Mind When Using the toLowerCase Method

The toLowerCase() method does a pretty straightforward thing: it creates a new string where all the uppercase letters are now lowercase. But there are a few things to keep in mind when using it. Let's take a look at them.

Strings are immutable

Strings are an immutable data type, which means they can't be changed. The original string will stay unchanged after you use the toLowerCase() method.

In the examples above, the toLowerCase() method has acted on the exampleString but never changed it. Checking the value of exampleString still shows the original value:

console.log(exampleString); // I am a string!

console.log(exampleString.toLowerCase()); // i am a string!

console.log(exampleString); // I am a string!

The toLowerCase() method returns a new string

This means that the toLowerCase()  method returns a new string. You'll need to save it in a variable if you want to use it again in your code.

const newString = exampleString.toLowerCase()

console.log(newString); // i am a string!

Strings are case sensitive

Strings are case sensitive, so a lowercase string is different than an uppercase string.

console.log('freecodecamp' === 'FREECODECAMP'); // false

This is useful when thinking about what the toLowerCase() method could be useful for. In the example you will see how this feature makes the toLowerCase() method useful and necessary when building a script or program that deals with strings.

toLowerCase() Method Example – How to Check if the User Input Matches

Let's write a small app that asks the user a question, gets the input, and gives feedback about the user's answer.

There are various ways to do that: you could use this in a web app, getting the value from an input element with type="text". To keep it simple, in the example you will see the usage of the prompt JavaScript function.

The prompt function will display a browser message popup with an input field in which the user can write an answer.

const answer = prompt("What color is the sun?")
if (answer.toLowerCase() === "yellow") {
  alert("Correct!")
} else {
  alert("That is not the correct color!")
}

This code asks the user a question, "What color is the sun?", and waits for an answer. Then it checks if the answer is "yellow", and if it is it prints "Correct!" If it isn't, it prints "That is not the correct color!".

But there is an issue with this code.

Running this code, you will have this question asked in the popup:

image-69

If you answer "Yellow", it says "That is not the correct color!"

Why does this happen?

Remember that strings are case sensitive. The script is checking if the user input the string yellowYellow, with a capital "Y", is a different string.

You can easily fix this by using the toLowerCase() method, and doing this small change to the code:

And now, if you try again...

image-70

What changed? Writing answer.toLowerCase() you make sure that the checked string is completely lowercase before comparing it with the correct answer string "yellow". In this way it doesn't matter if the user writes "YELLOW" or "yELLOW" or "yellow" – it is all converted to lowercase.

Thanks for reading! Now you know how to use the toLowerCase() method in JavaScript.