Load the first 5 bytes of a file with a jQuery ajax request. Beforehand, check whether the Range header is supported.

index.js

$(document).ready(function () {
    $.ajax({
        success: function (data, status, jqxhr) {
            if (jqxhr.getResponseHeader("Accept-Ranges") == "bytes") {
                $.ajax({
                    headers: {
                        "Range": "bytes=0-4"
                    },
                    success: function (data) {
                        $("pre").text(data);
                    },
                    type: "GET",
                    url: "some_local_file"
                });
            } else {
                alert("Range header not supported.");
            }
        },
        type: "HEAD",
        url: "some_local_file"
    });
});