JavaScript toUpperCase() method explained

Posted on Mar 16, 2022

How to use the toUpperCase() method in JavaScript

The JavaScript toUpperCase() method is a built-in method of the String prototype object that allows you to convert a string into its all uppercase version.

In the example below, the string good morning is transformed using the toUpperCase() method:

let myString = "good morning";

console.log(myString.toUpperCase());
// GOOD MORNING

The toUpperCase() method accepts any valid string, but this method won’t have any effect if you pass a number as a string like this:

"50".toUpperCase();
// returns '50'

Using the toUpperCase() method, you can capitalize the first letter of a sentence with the following code:

function upperCaseFirstLetter(str) {
  return str.charAt(0).toUpperCase() + str.substring(1);
}

let myString = "good morning";

let newString = upperCaseFirstLetter(myString);

console.log(newString); // Good morning

The first letter G in the string above is capitalized while the rest remain in lowercase.

You can also capitalize the first letter of every word by creating a custom function that makes use of the toUpperCase() method.

First, you need to split your string sentence into an array:

let strArray = myString.split(" ");

Next, you need to map() over the array and capitalize the first letter with the upperCaseFirstLetter() function above:

strArray = strArray.map((str) => {
  return upperCaseFirstLetter(str);
});

Finally, you need to join the strArray back into a single string with the join() method.

The full code is as shown below:

function upperCaseFirstLetter(str) {
  return str.charAt(0).toUpperCase() + str.substring(1);
}

let myString = "good morning";

let strArray = myString.split(" ");

strArray = strArray.map((str) => {
  return upperCaseFirstLetter(str);
});

let newString = strArray.join(" ");

console.log(newString); // Good Morning

The code to capitalize the string can be extracted as a function like this:

function upperCaseFirstLetter(str) {
  return str.charAt(0).toUpperCase() + str.substring(1);
}

function capitalizeWords(sentence){
  let strArray = sentence.split(" ");

  strArray = strArray.map((str) => {
    return upperCaseFirstLetter(str);
  });

  return strArray.join(" ");
}

let myString = "good morning you awesome human!";

console.log(capitalizeWords(myString));
// Good Morning You Awesome Human!

And that’s how you can capitalize a sentence using JavaScript toUpperCase() method.

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