How to convert string to lowercase in TypeScript?

In this tutorial, we will learn to convert a string into lowercase in TypeScript. Converting string to lowercase is a basic operation, but it is useful many times.

We can think about implementing the search functionality in the app. When users search for any phrase or word in lowercase, uppercase, or mixed case, we need to convert the string into lowercase and then execute the search query in the database to find the related items.

Using the toLowerCase() Method

The toLowerCase() method allows us to convert all alphabetic characters of the string into lowercase. If a character is in uppercase, it converts it to lowercase. Otherwise, it remains as it is. Also, it doesn’t change the special characters or numbers.

Users can follow the syntax below to convert the string to lowercase using the toLowerCase() method in TypeScript.

Syntax

let str: string = "TutorialsPoint";
str = str.toLowerCase();

In the above syntax, we have invoked the toLowerCase() method on the string, which means the object of the string class.

Example 1

In the example below, we convert a string to lowercase. The string contains only alphabets with some uppercase letters.

let str: string = "Welcome to TutorialsPoint";
console.log("Before: " + str);
str = str.toLowerCase();
console.log("After: " + str);

On compiling, it will generate the following JavaScript code −

var str = "Welcome to TutorialsPoint";
console.log("Before: " + str);
str = str.toLowerCase();
console.log("After: " + str);

The above code will produce the following output −

Output

Before: Welcome to TutorialsPoint
After: welcome to tutorialspoint

Example 2

In the example below, we convert a string to lowercase. The string contains alphanumeric chars and some special chars.

// String with alphanumeric chars
let str: string = "Tut123Point";
str = str.toLowerCase();
console.log(str);

// String with special chars
str = "Tut1:,.Point@3";
str = str.toLowerCase();
console.log(str);

On compiling, it will generate the following JavaScript code −

// String with alphanumeric chars
var str = "Tut123Point";
str = str.toLowerCase();
console.log(str);

// String with special chars
str = "Tut1:,.Point@3";
str = str.toLowerCase();
console.log(str);

The above code will produce the following output −

Output

tut123point
tut1:,.point@3

Custom Algorithm to Convert String to Lowercase

The other way to convert a string to lowercase in TypeScript is that iterate through every character of the string and convert every character in lowercase.

Steps

STEP 1 − Define two string-type variables. Assign the original string value to the first variable. We will assign the converted string to the second variable.

STEP 2 − Next, we use the for loop to iterate through the string characters. For every character, we find the ASCII value using the charCodeAt() method of the string. If we find an ASCII value between 65 and 90 (including), the alphabetic character is in uppercase, and we need to convert it into lowercase.

STEP 3 − To convert uppercase characters to lowercase, add 32 to the ASCII value of uppercase later, and use the fromCharCode() method of the string class to get a character from its ASCII value.

STEP 4 − Append the converted character to the second string and, at last, printing the lower string.

Example

In the example below, we convert a string containing some uppercase letters to lowercase.

let stringName: string = "Hi @312 User! Are YOU THERE?";
let lower: string = "";

for (let i = 0; i < stringName.length; i++) {
   let value = stringName.charCodeAt(i);
   if (value >= 65 && value <= 90) {
      lower += String.fromCharCode(value + 32);
   } else {
      lower += stringName[i];
   }
}
console.log(lower);

On compiling, it will generate the following JavaScript code −

var stringName = "Hi @312 User! Are YOU THERE?";
var lower = "";
for (var i = 0; i < stringName.length; i++) {
   var value = stringName.charCodeAt(i);
   if (value >= 65 && value <= 90) {
      lower += String.fromCharCode(value + 32);
   }
   else {
      lower += stringName[i];
   }
}
console.log(lower);

The above code will produce the following output &miinus;

hi @312 user! are you there?

Users learned two ways to convert the string into lowercase. The first way is the simplest, as we need to write a single line of code. The second method demonstrates how the toLowerCase() method is implemented manually in the string class. So, it is recommended to use the first method. The second method is only to demonstrate how the toLowerCase() method works internally.

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