好的，在堆垛机的帮助下，我能够得到一条错误消息，显示在输入表单下面。
我需要的是，当用户在表单中输入任何输入时，不会显示错误消息。我做错了什么？
这是html

<form id="url">
        <input type="text" name="urlName">
        <input type="submit" value="Build Your App"></input>
    </form>
    <div id="error-message">

    </div>

这是js

document.getElementById("url").addEventListener("submit", (event) => {
            event.preventDefault()
            let errorMessage = document.getElementById("error-message").innerHTML = "Please provide your store URL";
            let myForm = document.getElementById("url");
            let formData = new FormData(myForm);
            if (formData.get("urlName") === "")
            return errorMessage;
            EndOfUrl = sanitizeDomainInput(formData.get("urlName"));
            newUrl = redirectLink(EndOfUrl);
            window.location.href = newUrl;
            return false;
        });

    function sanitizeDomainInput(input) {
        input = input || 'unknown.com'
        if (input.startsWith('http://')) {
            input = input.substr(7)
        }
        if (input.startsWith('https://')) {
            input = input.substr(8)
        }
            var regexp = new RegExp(/^(([a-zA-Z]{1})|([a-zA-Z]{1}[a-zA-Z]{1})|([a-zA-Z]{1}[0-9]{1})|([0-9]{1}[a-zA-Z]{1})|([a-zA-Z0-9][a-zA-Z0-9-_]{1,61}[a-zA-Z0-9]))\.([a-zA-Z]{2,6}|[a-zA-Z0-9-]{2,30}\.[a-zA-Z]{2,3})$/)
            return regexp.test(input) ? input : 'unknown.com';

    }

    function redirectLink(domain) {
        return `https://dashboard.getorda.com/signup/?state=${domain}`;
    }