test.html

<html>
<head>

<script type='text/javascript'>
function post(url, data){
    x = new XMLHttpRequest()
    x.onreadystatechange = function(){
        console.log(x.responseText)
    }
    
    x.open('POST', 'http://localhost:5000/messages/'+url, true)
    x.setRequestHeader('Content-Type', 'application/x-www-form-urlencoded')
    x.send('message='+data)
}

function xhr(method, url, data, cb){
    x = new XMLHttpRequest()
    x.onreadystatechange = function() {
        cb(x.responseText)
    }
    
    x.open(method, 'http://localhost:5000/messages/'+url, true)
    
    if(method == 'POST'){
        x.setRequestHeader('Content-Type', 'application/x-www-form-urlencoded')
        data = 'message='+data
    }
    
    x.send(data)
    
}

function send(){    
    xhr('POST', 'test', document.forms[0].childNodes[1].value)
    
    return false
}

window.onload = function(){
    polling = setInterval(function(){poll()}, 2000)
}

function poll(){
    xhr('GET', 'test', null, function(text) {
        var pre = document.getElementById('log')
        pre.innerHTML = text
    })
}
</script>
</head>

<body>
    <pre id='log'>
        
    </pre>
    <form onsubmit='return send()'>
        <input id='textbox' type='text' />
    </form>
    