How to process each letter of text using JavaScript ?

Last Updated : 16 Aug, 2021

Given a string and the task is to process it character by character.

JavaScript String toUpperCase() Method: This method converts a string to uppercase letters.
Syntax:

string.toUpperCase()

Parameters: This method accepts single parameter str which is required. It specifies the string to be searched.
Return Value: It returns a string denoting the value of a string converted to uppercase.
JavaScript String charAt() Method: This method returns the character at the passed index in a string. The index of characters starts from 0.
Syntax:

string.charAt(index)

Parameters: This method accepts single parameter index which is required. It specifies the integer representing the index of the character to return.
Return Value: It returns a string, denoting the character at the passed index, or an empty string if the index number is invalid.

Example 1: This example processes the string letter by letter using for loop and converts each letter to uppercase separately.

html

<!DOCTYPE HTML> 
<html> 
    <head> 
        <title> 
            How to process each character of text
        </title>
    </head> 
    
    <body style = "text-align:center;"> 
    
        <h1 style = "color:green;" > 
            GeeksForGeeks 
        </h1>
    
        <p id = "GFG_UP" style = 
            "font-size: 15px; font-weight: bold;">
        </p>

        
        <button onclick = "gfg_Run()"> 
            check
        </button>
        
        <p id = "GFG_DOWN" style = 
            "color:green; font-size: 20px; font-weight: bold;">
        </p>

        
        <script>
            var el_up = document.getElementById("GFG_UP");
            var el_down = document.getElementById("GFG_DOWN");
            var str = "This is String";
            el_up.innerHTML = "String = '"+str + "'";
        
            function gfg_Run() {
                var str_Upper = "";
                for (var i = 0; i < str.length; i++) {
                    str_Upper += str.charAt(i).toUpperCase();
                }
                el_down.innerHTML = str_Upper;
            }         
        </script> 
    </body> 
</html>

Output:

Before clicking on the button:

After clicking on the button:

Example 2: This example processes the string letter by letter using for in loop and alerts each letter separately.

html

<!DOCTYPE HTML> 
<html> 
    <head> 
        <title> 
            How to process each letter of text
        </title>
    </head> 
    
    <body style = "text-align:center;"> 
    
        <h1 style = "color:green;" > 
            GeeksForGeeks 
        </h1>
    
        <p id = "GFG_UP" style = 
            "font-size: 15px; font-weight: bold;">
        </p>

        
        <button onclick = "gfg_Run()"> 
            check
        </button>
        
        <script>
            var el_up = document.getElementById("GFG_UP");
            var str = "str";
            el_up.innerHTML = "String = '" + str + "'";
        
            function gfg_Run() {
                for (var i in str) {
                    alert(" character = "+str.charAt(i));
                }
            }         
        </script> 
    </body> 
</html>