Bunpro: Hide Tense.user.js

// ==UserScript==
// @name         Bunpro: Hide Tense
// @namespace    http://tampermonkey.net/
// @version      0.0.3
// @description  Automatically hides the tense info in the missing phrase area
// @author       yndajas
// @include      *bunpro.jp/*
// @exclude      *community.bunpro.jp*
// @require      https://greasyfork.org/scripts/432418-wait-for-selector/code/Wait%20For%20Selector.js?version=974366
// @require      https://greasyfork.org/scripts/370623-bunpro-helpful-events/code/Bunpro:%20Helpful%20Events.js?version=974369
// @grant        none
// ==/UserScript==

(() => {
    // btw works for both reviews and cram sessions
    let hintText;
    const placeholder = "_________";
    // wait until we're reviewing
    $('HTML')[0].addEventListener('quiz-page', function () {
        $('HTML')[0].addEventListener('new-review-item', function(e) {
            // get element
            const studyAreaInput = document.getElementsByClassName("study-area-input")[0];
            let studyAreaText = studyAreaInput.getAttribute("data-tense");
            // event fires multiple times per review item, so we have to make addiional check if hint was already hidden
            if (studyAreaText && studyAreaText != placeholder) {
                hintText = studyAreaText;
                // replace hint attribute
                studyAreaInput.setAttribute("data-tense", placeholder);
            }
            function setHint(event){
                if (event.keyCode == 32 && studyAreaInput.getAttribute("data-tense") == placeholder) {
                    studyAreaInput.setAttribute("data-tense", hintText);
                    event.stopPropagation();
                }
            };
            // show hint back when we press space without focus on answer
            $("body").keydown(setHint);

            // show hint back when we press space typing in answer field
            $("#study-answer-input").keydown(setHint);

        });
    })
})();