username_validation_native.js

async function validateUsername(username) {
    const errorNode = document.getElementById("error-text");

    // Check if username is a non-empty string
    if (typeof username !== "string" || username.trim() === "") {
        errorNode.innerText = "Username is required";
        return false;
    }

    // Check if username format is valid
    if (!username.match(/^\w+$/)) {
        errorNode.innerText = "Username must consist of characters and numbers";
        return false;
    }

    // Check if username is unique.
    const response = await fetch(`/api/checkusername/${username}`); // returns { available: true | false }
    const { available } = await response.json();
    if (!available) {
        errorNode.innerText = `Username is already taken`;
        return false;
    }

    return true;
}


// Call the function
validateUsername("test").then((valid) => {
    // continue with registration if valid
});