How to use String.prototype.repeat() and String.prototype.startsWith() In Javascript

1. Using Regular Expression with test() method

3. Using String Rotation and Concatenation

This approach repeats a substring until it equals the input string’s length. Then, it checks if the input string starts with this repeated substring, indicating that the string is entirely made up of the same substring.

Example:

JavaScript

function isEntirelyMadeUpOfSameSubstring(str) {
    const len = str.length;
    for (let i = 1; i <= len / 2; i++) {
        const substring = str.substring(0, i);
        if (substring.repeat(len / i) === str) {
            return true;
        }
    }
    return false;
}


console.log(isEntirelyMadeUpOfSameSubstring("abcabcabc")); // Output: true
console.log(isEntirelyMadeUpOfSameSubstring("abcdefg"));  // Output: false