HTML's datalist element autocompletes. This script is my attempt to get it to autosubmit as well.

submitFormFromDatalist.js

// Licensed under a CC0 1.0 Universal (CC0 1.0) Public Domain Dedication
// http://creativecommons.org/publicdomain/zero/1.0/

(function (win, doc) {
    'use strict';
    // Cut the mustard
    if (!doc.querySelectorAll || !doc.querySelectorAll('input[list]') || !win.HTMLDataListElement || !win.addEventListener){
        return;
    }
    // Loop through each input element with a list attribute
    doc.querySelectorAll('input[list]').forEach( function (formfield) {
        // Find the corresponding datalist element
        var datalist = doc.getElementById(formfield.getAttribute('list'));
        // Store the character count of the input element's value
        var lastlength = formfield.value.length;
        // Run this function when the input element's value is updated
        var checkInputValue = function (inputValue) {
            // If the current character count is longer by the last character count by more than one, check the datalist
            if (inputValue.length - lastlength > 1) {
                // Loop through each option element in the datalist
                datalist.querySelectorAll('option').forEach( function (item) {
                    // If the value of the option matches the input's current value, submit the form
                    if (item.value === inputValue) {
                        formfield.form.submit();
                    }
                });
            }
            // Update the character count
            lastlength = inputValue.length;
        };
        // Run that function every time the input element is updated
        formfield.addEventListener('input', function () {
            checkInputValue(this.value);
        }, false);
    });
}(this, this.document));

Blog post: Submitting a form with datalist