As an admin, sometimes you might need to clear a field that is set as readonly in the UI. And for fields like Date Date/Time you can't just go to the list view and clear them like text fields. I wanted an alternative to having to making a GlideRecord script just to clear the field. So I decided to add a context menu option to do this (for admins only).

The field context menu is all in an OOTB UI Macro (element_context) that I didn't want to customize and risk missing future updates. But I am leveraging GwtContextMenu() that is instantiated in that UI Macro. This is not future proof because it listens for a DOM element with a certain class to appear which happens when you right click on a label. It then tacks on the additional element for the Clear Field option.

This is a Global UI Script but is limited to admins and only runs on forms. There is room for improvements so feel free to contribute. Enjoy!

jQuery(document).ready(function() {
    //only do this for admins
    if (g_user.hasRole('admin')) {

        //only do this on forms
        if (typeof g_form != 'undefined') {
            //listen for field context menu and add option to clear field
            onElementInserted('body', '.context-menu-minwidth', function(element) {
                var menu = jQuery('.context-menu-minwidth');

                //only do this if the context menu is for a field
                if(menu.next().text()=='Configure Label'){

                    //there is probably a better way to find the field name
                    var field = menu.siblings().last().text().replace('Watch - \'','').replace('\'','');
                    gcm.addLine();
                    //gcm.addHref([label],[javascript function])
                    gcm.addHref("Clear Field", "g_form.setValue('"+field+"', '');");
                }
            });     
        }
    }
});

function onElementInserted(containerSelector, elementSelector, callback) {

    var onMutationsObserved = function(mutations) {
        mutations.forEach(function(mutation) {
            if (mutation.addedNodes.length) {
                var elements = $j(mutation.addedNodes).find(elementSelector);
                for (var i = 0, len = elements.length; i < len; i++) {
                    callback(elements[i]);
                }
            }
        });
    };

    var target = $j(containerSelector)[0];
    var config = {
        childList: true,
        subtree: true
    };
    var MutationObserver = window.MutationObserver || window.WebKitMutationObserver;
    var observer = new MutationObserver(onMutationsObserved);
    observer.observe(target, config);

}