FocusInput

focusinput.user.js

// ==UserScript==
// @name         FocusInput
// @namespace    https://berkantkz.github.io
// @version      0.1
// @description  Focus to the very first text input on a web page on any key press
// @author       berkantkz
// @match        *://*/*
// @homepage     https://gist.github.com/berkantkz/cfa31157d8e54d821f1ddf345a93d36a
// @icon         https://berkantkz.github.io/kz.png
// @grant        none
// ==/UserScript==

(function() {
    'use strict';

    // feature to disable certain key detections on certain websites.
    // keys array must be placed in order with the website index in hosts array.
    // e.g. berkantkz.live is the 1st item in the array. so the keys that will be
    // dismissed on that page must be in the 1st array in keys array which is "a"
    // and "b" keys in the variables below.

    var hosts = ["youtube.com", "berkantkz.live"];
    var keys = [["j","k","l","t","c","f","m"], ["a","b"]];
    var currentHost = window.location.host.replace('www.','');

    document.onkeypress=function(k) {
        //console.log(k);
        if (k.code !== "Space"){

            if (hosts.includes(currentHost) && keys[hosts.indexOf(currentHost)].includes(k.key)) return;
            if (document.activeElement.tagName == "INPUT" || document.activeElement.tagName == "TEXTAREA" || document.activeElement.contentEditable == "true") return;

            var i;
            var item = document.getElementsByTagName('input');
            var l = document.getElementsByTagName('input').length;
            var n;

            for (i=0; i<l; i++) {
                if (item[i].placeholder !== '' || item[i].value !== '' && item[i].type == "text" || item[i].value == "search") {
                    //console.log(item[i]);
                    n = item[i];
                    break;
                }
            }

            if (n !== document.activeElement) {
                n.value = "";
                n.click();
                n.focus();
            }
        }
    };
})();

Usually, search boxes are the first input elements of web pages. And sometimes, I am too lazy to move my cursor onto them. I made this script so as not to remove my hand from my keyboard and be in need to use the mouse in order to click search text field. I can simply focus on any object other than input or text area and start typing and keep searching right away.

Added option to dismiss certain keys in certain hosts.