templates/index2.html

<doctype html>
    <html>

    <head>

        <link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/font-awesome/4.7.0/css/font-awesome.min.css">
    </head>

    <body>
        <link href='../static/css/main.css' rel='stylesheet'>
        <div class='header'> Web Vulnerablity Scanner Framework</div>
        <div class='bodypart'>
            <form method="POST" id="myform" action="">
                <select class="option" data-trigger="" name="choices-single-defaul" id="attack" onchange=setAction();>
                <option >What to Perform</option>
                <option value="xss">XSS Test</option>
                <option value="sql">SQL Injection check</option>
                <option value="ports">Port Scan</option>
                <option value="subdomain">Domain Scan</option>
                <option value="discover">File path traversal</option>
                <option value="fullscan">Complete scan</option>
              </select>

                <input id="search" class='entervalues' name="ipaddress" type="text" placeholder="Enter your IP or web-adress" />
                <button type='submit'><i class="fa fa-search"></i></button>

            </form>
        </div>

        <script>
            function setAction() {
                var attackType = document.getElementById('attack').value;
                // alert(attackType);
                var formAction = document.getElementById('myform');
                formAction.action = attackType;
                if (attackType == "xss") {
                    search = document.getElementById("search");
                    search.placeholder = "Please enter full url like abc.com";
                } else if (attackType == "discover") {
                    search = document.getElementById("search");
                    search.placeholder = "Please enter pnly domain name e.g abc.com";
                } else {
                    search = document.getElementById("search");
                    search.placeholder = "Please enter IP or URL";
                }
            }
        </script>

    </body>

    </html>