fetch.html

<!DOCTYPE html>
<html>
    <head>

    </head>
    <body>
        <script>
            (async function(){
                const button = document.createElement('button');
                const urlField = document.createElement('input'); 
                urlField.type = 'text'; 
                urlField.value = 'http://localhost:8000';
                urlField.style.width = '400px';  
                button.innerText = 'Press'; 
                button.style.width = '400px'; 

                const body = document.body; 

                body.appendChild(urlField); 
                body.appendChild(button); 

                button.addEventListener('click', async () => {
                    const time = performance.now(); 
                    const response = await fetch(urlField.value, { mode: 'no-cors'}); 
                    const result = await response.blob(); 
                    button.innerText = `Time: ${performance.now() - time} ms, Bytes: ${result.size}`; 
                    console.log(result); 
                })
            })()
        </script>
    </body>
</html>