Untitled

<!DOCTYPE html>
<html>
<head>
    <meta charset="utf-8">

<script>

function compare(a, b) {
    if (a.length > b.length)
        return 1;
    else if (a.length < b.length)
        return -1;
    else
        return 0;
}

function test() {
    document.getElementById("b").innerHTML = "";
    strs = document.getElementById("a").value.split(" ");
    strs.sort(compare);
    for (var i = 0; i < strs.length; ++ i) {
        document.getElementById("b").innerHTML += strs[i] + " ";
    }
}

</script>

</head>
<body>
    <input type="text" id="a">
    <button onclick="test()">Ввод</button>
    <p id="b"></p>
</body>
</html>