JavaScript: Input a string and converts upper case letters to lower and vice versa

JavaScript String: Exercise-10 with Solution

Write a JavaScript function that takes a string with both lowercase and upper case letters as a parameter. It converts upper case letters to lower case, and lower case letters to upper case.

Test Data:
console.log(swapcase('AaBbc'));
"aAbBC"

Visual Presentation:

Sample Solution:

JavaScript Code:

// Define a function named swapcase that takes a string str as input
swapcase = function swapcase(str) {
    // Use the replace method with a regular expression to match lowercase and uppercase letters separately
    return str.replace(/([a-z]+)|([A-Z]+)/g, function(match, chr) {
        // For each match, if chr (lowercase letter) exists, convert it to uppercase; otherwise, convert the match (uppercase letter) to lowercase
        return chr ? match.toUpperCase() : match.toLowerCase();
    });
}
// Output the result of applying the swapcase function to the string 'AaBbc'
console.log(swapcase('AaBbc'));

Output:

aAbBC

Explanation:

In the exercise above,

• The function "swapcase()" is declared, taking a string 'str' as input.
• Inside the function, a regular expression is used to match lowercase and uppercase letters separately.
• The "replace()" method is applied to the string 'str', replacing each match:
• If the match is a lowercase letter ('([a-z]+)'), it is replaced with its uppercase equivalent.
• If the match is an uppercase letter ('([A-Z]+)'), it is replaced with its lowercase equivalent.
• The modified string is returned by the function.
• Finally, the console.log statement calls the "swapcase()" function with the string 'AaBbc' as input and outputs the result.

Flowchart:

Live Demo:

See the Pen JavaScript Input a string and converts upper case letters to lower and vice versa - string-ex-10 by w3resource (@w3resource) on CodePen.

Improve this sample solution and post your code through Disqus.

Previous: Write a JavaScript function to capitalize the first letter of each word in a string.
Next: Write a JavaScript function to convert a string into camel case.