Is there a way to "inject" a custom keyboard shortcut into a page on load?

Question

I'm looking into creating a custom keyboard shortcut for myself browsing reddit.

My plan is to create an event listener to listen for a certain key chord and then toggle a switch in RES. I haven't been able to find a way to "inject"(not sure if I'm using the right word) when I load Reddit.

I would like this shortcut to toggle the Nightmode(or other switches) on keypress.

Answer 1

I found out a way to do it using a Chrome extension called "Tampermonkey".

Here's the code I used:

    var eventUtility = {
        addEvent : function(el, type, fn) {
            if (typeof addEventListener !== "undefined") {
                el.addEventListener(type, fn, false);
            } else if (typeof attachEvent !== "undefined") {
                el.attachEvent("on" + type, fn);
            } else {
                el["on" + type] = fn;
            }
        }
    };


    (function() {
        eventUtility.addEvent(document, "keydown",
            function(evt) {
                var code = evt.keyCode,
                shiftKey = evt.shiftKey;

                //Shift Key + N
                if (shiftKey && code === 78) {
                    if(document.getElementById('night mode')){
                        document.getElementById('night mode').click();
                    } else {
                        document.getElementById('RESSettingsButton').click();

                        var toggleFilter = function() {
                          document.getElementById('night mode').click();
                        };
                        setTimeout(toggleFilter, 50);
                    }
                }
            });
    }());