Example code style with comments (comments are meant to explain code style do not use comments like this in application)

Theme javascript.js

function initToggle({
    TOGGLE_SELECTOR = ".js-toggle",
    TOGGLE_FOCUSED_CLASS = "toggle--focused",
    TOGGLE_ITEM_OPEN_CLASS = "toggle__item--open", // use constants for class names and selectors variable name should end with _CLASS or _SELECTOR
}) { // use init functions that encapsulate functionality
    const $toggle = $(TOGGLE_SELECTOR); // jQuery objects variable names should start with $ for jQuery elements

    $toggle.on("focus", (event) => {
        const $this = $(event.currentTarget);
        $this.addClass(TOGGLE_FOCUSED_CLASS);
    });
    $toggle.on("focusout",(event) => {
        const $this = $(event.currentTarget);
        $this.addClass(TOGGLE_FOCUSED_CLASS);
    });
 
    function toggleItemOpen($toggleElement) { // create functions for code used multiple times and name them properly
        const toggleItemSelector = $toggleElement.data("toggleItem"); // variables holding selectors should end with _Selector
        const $toggleItem = $toggleElement.find(toggleItemSelector); // use cashed selectors if possible

        if ($toggleItem.hasClass(TOGGLE_ITEM_OPEN_CLASS)) {
            $toggleElement.setAttribute("aria-expanded", false);
            $toggleItem
                .removeClass(TOGGLE_ITEM_OPEN_CLASS)
                .slideUp();

            return; // better to use early return over else block
        }

        $toggleElement.setAttribute("aria-expanded", true);
        $toggleItem
            .addClass(TOGGLE_ITEM_OPEN_CLASS);
            .slideDown();
    }

    $toggle.click((event) => {
        $toggleElement = $(event.currentTarget); // use named this
        toggleItemOpen($toggleElement);
    });

    const ENTER_KEY = 13; // name unclear constants
    $toggle.keypress((event) => { // elements with onClick have to have key press as well
        $toggleElement = $(event.currentTarget); // use named this
        switch (event.which) {
            case ENTER_KEY:
                toggleItemOpen($toggleElement);
        }
    });
}


$(document).ready(() => { // keep the document ready simple as possible
    initToggle(); // only init functions in document ready
});