test.js

TXTextControl.addEventListener("ribbonTabsLoaded", function () {
   addCustomContextMenu();
});

function addCustomContextMenu() {
    let myMenuItem =
    {
        "__id": "myMenuItem",
        "isChecked": false,
        "isEnabled": true,
        "text": "",
        "imageUrl": "data:image/svg+xml;base64,PD94bWwgdmVyc2lvbj0iMS4wIiBlbmNvZGluZz0idXRmLTgiPz4NCjwhLS0gR2VuZXJhdG9yOiBBZG9iZSBJbGx1c3RyYXRvciAyNi41LjAsIFNWRyBFeHBvcnQgUGx1Zy1JbiAuIFNWRyBWZXJzaW9uOiA2LjAwIEJ1aWxkIDApICAtLT4NCjxzdmcgdmVyc2lvbj0iMS4xIiBpZD0iTGF5ZXJfMSIgeG1sbnM9Imh0dHA6Ly93d3cudzMub3JnLzIwMDAvc3ZnIiB4bWxuczp4bGluaz0iaHR0cDovL3d3dy53My5vcmcvMTk5OS94bGluayIgeD0iMHB4IiB5PSIwcHgiDQoJIHZpZXdCb3g9IjAgMCAxNiAxNiIgc3R5bGU9ImVuYWJsZS1iYWNrZ3JvdW5kOm5ldyAwIDAgMTYgMTY7IiB4bWw6c3BhY2U9InByZXNlcnZlIj4NCjxzdHlsZSB0eXBlPSJ0ZXh0L2NzcyI+DQoJLnN0MHtmaWxsOiNGRjAwRkY7fQ0KCS5zdDF7ZmlsbDojOUIwMEZGO30NCjwvc3R5bGU+DQo8Zz4NCgk8cmVjdCB4PSIxLjUiIHk9IjEuNSIgY2xhc3M9InN0MCIgd2lkdGg9IjEzIiBoZWlnaHQ9IjEzIi8+DQoJPHBhdGggY2xhc3M9InN0MSIgZD0iTTE0LDJ2MTJIMlYySDE0IE0xNSwxSDF2MTRoMTRWMUwxNSwxeiIvPg0KPC9nPg0KPC9zdmc+DQo=",
        "dropDownIsScrollable": false,
        "items": [],
        "clickHandler": ClickMe
    };

    let mySeparator =
    {
        "__id": "mySeparator",
        "isChecked": false,
        "isEnabled": true,
        "text": "",
        "imageUrl": "",
        "dropDownIsScrollable": false,
        "items": [],
    };

    TXTextControl.addEventListener("contextMenuOpening", function (menu) {

        myMenuItem.text = "Custom Context Menu Item. Location: " + menu.location;

        menu.items.push(mySeparator);
        menu.items.push(myMenuItem);
    })

    function ClickMe() {
        alert("Custom Click Event");
    }
}