Emulate Emacs text editing in browser

emacs_text_movement.js

// ==UserScript==

(function () {
    'use strict';

    let nowPlayingClassName = 'now-playing-tracklist-row'
    let buffer = [];
    let bindings = [
        {binding: ["control", "f"], action: moveForward},
        {binding: ["control", "b"], action: moveForward}

    ];

    function moveCaret(win, charCount) {
        var sel, range;
        if (win.getSelection) {
            sel = win.getSelection();
            if (sel.rangeCount > 0) {
                var textNode = sel.focusNode;
                var newOffset = sel.focusOffset + charCount;
                sel.collapse(textNode, Math.min(textNode.length, newOffset));
            }
        } else if ( (sel = win.document.selection) ) {
            if (sel.type != "Control") {
                range = sel.createRange();
                range.move("character", charCount);
                range.select();
            }
        }
    }

    function moveForward () {
        moveCaret(window, 1);
    }

    function moveBackward () {
        moveCaret(window, -1);
    }


    Array.prototype.last = function () {
        return this[this.length - 1];
    }

    function arraysMatch(arr1, arr2) {
        if (arr1.length !== arr2.length) {
            return false;
        }
        for (let i = 0; i < arr1.length; i++) {
            if (arr1[i] !== arr2[i]) return false;
        }
        return true;
    }



    // register handling for keybindings
    document.getElementById("editable").addEventListener('keydown', event => {
        let key = event.key.toLowerCase();
        if (key == 'control') {
            buffer = [];
        }
        console.log(key);
        if (buffer.last() != key) {
            buffer.push(key);
        }
        bindings.filter(function (item) {
            if (arraysMatch(item.binding, buffer)) {
                item.action();
            }
        });
    });

})();