type-guard.js

// ==UserScript==
// @name         Type Guard
// @namespace    http://tampermonkey.net/
// @version      0.1
// @description  try to take over the world!
// @author       Chuang Yu
// @match        *://*/*
// @icon         https://www.google.com/s2/favicons?sz=64&domain=google.com
// @grant        none
// ==/UserScript==

(function () {
    "use strict";

    // Get all text boxs including inputs and textareas
    const textboxes = document.querySelectorAll("input, textarea");

    function setCache(key, value) {
        localStorage.setItem(key, value);
    }

    function getCache(key) {
        return localStorage.getItem(key);
    }

    // Generate a unique id based on the input's properties
    // Even after the page is refreshed, the id will be the same
    function generateId(element) {
        return element.id || element.name || element.placeholder;
    }

    // Save the value to cache
    function onInput(event) {
        const id = generateId(event.target);
        // Update the value only when it's not empty. This is to avoid accidentally clear up the input box or leave a space but press enter key
        if (event.target.value !== undefined && event.target.value !== null && event.target.value.trim() !== "") {
            setCache(id, event.target.value);
        }
    }

    // When pressing cmd + shift + p, retrieve the value from cache to the active input
    function onKeyCombo(event) {
        if (event.metaKey && event.shiftKey && event.key === "p") {
            event.preventDefault();
            const id = generateId(event.target);
            const value = getCache(id);
            event.target.value = value;
        }
    }

    let loaded = false;
    if (!loaded) {
        // Listen to all input events
        for (var i = 0; i < textboxes.length; i++) {
            textboxes[i].addEventListener("input", onInput);
            textboxes[i].addEventListener("keydown", onKeyCombo);
        }
        loaded = true;
    }

    console.log("Type Guard Loaded");
})();