Programmatically control a Desmos graph

DesmosPlayer.user.js

// ==UserScript==
// @name          desmosPlayer
// @namespace     http://github.com/jason-woolf
// @version       1.0.0
// @description   Program a series of graph changes to create animation
// @author        Jason Woolf (MathyJaphy)
// @match         https://www.desmos.com/calculator*
// @grant         none
// @run-at        document-idle
// ==/UserScript==

// LICENSE: ISC
// Fork of https://gist.github.com/jared-hughes/b62dc3042947d6dcee16a186301227dc

"use strict"

/*****************************************************************************
// Example 1: MathyJaphy Intro/Logo
// Graph for this example: https://www.desmos.com/calculator/y3lulgdmir
//
// This is the animation of my channel logo that I used in this video:
// https://youtu.be/sV1NbgNodD0

// Helpful symbolic names for expression ID's
const a = 116
const b1 = 139
const b2 = 140
const b3 = 141
const b4 = 142
const f1 = 131
const f2 = 133
const f3 = 136
const f4 = 138
const f5 = 128
const name_angle = 144
const name_size = 145
const boing = 148
const w1 = 775
const w2 = 776

// Define the program
const mathyJaphy = [
    startSlider(b1, 1000),
    startSlider(b2, 1000),
    startSlider(b3, 1000),
    startSlider(b4, 1000),
    startSlider(w1),
    animateValue(w2, 0, 1.5, 0.1, 0, 3000),
    animateValue(w2, 1.5, 0, 0.07, 0, 1000),
    stopSlider(w1),
    startSlider(f1, 1000),
    startSlider(f2, 1000),
    startSlider(f3, 1000),
    startSlider(f4, 1000),
    startSlider(f5, 3000),
    [startSlider(name_angle),
     startSlider(name_size)],
    pause(2500),
    startSlider(boing)
]

// Run it
desmosPlayer(mathyJaphy, {graphTitle: "MathyJaphy", debugMode: true});

******************************************************************************/

/*****************************************************************************
// Example 2: Binary Counter
// Graph for this example: https://www.desmos.com/calculator/o61fs3lfjb
//
// A simple binary counter with "lights" for each bit. I wanted to see how
// intricate a program I could create with the goto/label instructions.

// Helpful symbolic names for expression ID's
const ones = 8;
const twos = 6;
const fours = 4;
const eights = 2;

// Define the program
const binaryCounter = [
    label("clear eights"),
    hide(eights),
    label("clear fours"),
    hide(fours),
    label("clear twos"),
    hide(twos),
    label("clear ones"),
    hide(ones),
    pause(1000),
    show(ones),
    pause(1000),
    show(twos),
    goto("clear ones", 1),
    show(fours),
    goto("clear twos", 1),
    show(eights),
    goto("clear fours", 1),
    goto("clear eights"),
]

// Run it
desmosPlayer(binaryCounter, {graphTitle: "Binary Counter", debugMode: true});

******************************************************************************/


// DesmosPlayer - a module for controlling Desmos graphs for
// making animated videos or whatever.
//
// Function: desmosPlayer
// Parameters:  program - an array of functions to be executed
//                        in sequence that control expressions
//                        in a Desmos graph.
//              properties - An object that conveys additional
//                           configuration parameters.
//
// This is the main function of the DesmosPlayer module.  It sets up the
// environment needed to run the given program.  Create a program by
// filling an array with the results of "instruction functions" (see
// examples above).  Then pass this program to the desmosPlayer function,
// along with optional properties:
//
//     graphTitle: A string value that has to match the title of the graph
//                 in order for the system to be activated.
//     allowSave:  If set to true, do not disable the "save" button after
//                 the program has started.  It is normally disabled to
//                 prevent accidental modification to the initial state.
//     debugMode:  Set to 'true' to enable back-stepping.
//
// A "Start" button will be added next to the "Save" button.
// Clicking it will start the program and turn it into a "Stop"
// button.  Clicking it again will stop execution of the program.  A
// "Reset" button will also appear which when clicked will put the graph and
// the running program back to their initial states so that the program can
// be run again.  Note: if allowSave mode is on and the save button is
// accidentally used to overwrite the original graph after the program has
// run, hit the "Reset" button and save again.  There is also a "Step"
// button which will execute one function in the program at a time.  If
// debugMode is true, then a "Back Step" button also appears after the
// program has started, allowing you to undo the effect of the previous
// step, all the way back to the start of the program. This is expensive
// since it saves the entire graph state after every step.
//
// Each instruction takes one or more expression ID parameters, which are
// not the same as the index of the expression displayed in the expression
// list. To get the ID of an expression, select it and press ctrl-Q.  The ID
// will appear in the console window.  Normally these are numbers, but they
// could be strings if the expressions were created by your program (see the
// set command below).
//
// Execution of the instructions proceeds automatically from one to the next.
// The pause() instruction can be used to insert delays.  Also, most
// instructions take an optional delay value as the final parameter which
// inserts a pause implicitly.
//
// Instructions can be grouped together using square brackets.  Instructions
// in such groupings will be run without delays and without giving Desmos a
// chance to update its graph until they have all run.  This can eliminate
// glitches in the graph and make it look as though the instructions ran
// simultaneously.  For example:
//
//    const testProg = [
//       startSlider(1, 5000),
//       [setValue(1, 0),
//        setValue(2, 1.0),
//        setValue(3, 2.5),
//        hideLabel(3),
//        showLabel(4)],
//       startSlider(1, 5000)
//    ]
//
// In this hypothetical scenario, a slider runs once to animate something
// and then it is reset and a bunch of other elements are altered, hidden
// and revealed all at once, then the animation is run again.  Without the
// grouping, intermediate settings might be visible as glitches.  Delays
// within the grouped commands are ignored, and animateValue instructions
// will go directly to the ending value.  It is an error to have a goto
// instruction inside a grouping.
//
// When each instruction is executed, a message is displayed in the console
// so it is possible to see what the program is doing.  When back-stepping,
// the console will show the instruction that was just undone.
//
// Here is a summary of the instructions.  Detailed descriptions appear above
// each instruction function in the code below.
//
//    hide (<id>, [<id>, ...])
//    show (<id>, [<id>, ...])
//    hideLabel (<id>, [<id>, ...])
//    showLabel (<id>, [<id>, ...])
//    setLabel (<id>, <label-string>)
//    setValue (<id>, <value>, [<delay>])
//    startSlider (<id>, [<delay>])
//    stopSlider (<id>, [<delay>])
//    animateValue (<id>, <start-value>, <end-value>, <increment>, [<frame-delay>], [<delay>])
//    setSliderProperties (<id>, {<properties>}, [<delay>])
//    set (<id>, <properties>, [<delay>])
//    stop (<message-string>)
//    pause (<delay>)
//    label (<label-name-string>)
//    goto (<label-name-string>, [<repeat-count>])

// Instruction: hide
// Parameter: ids - comma separated list of expression id's to hide
// Hides all the expressions given as arguments to the instruction.
// Equivalent to set(id, {hidden: true}) for each of the given id's.
// Moves on to the next instruction immediately.
function hide (...ids) {
    let verify = 1;
    const func = () => {
        if (verify) {
            verify = 0;
            for (let id of ids) {
                verifyId(id);
            }
        }
        for (let id of ids) {
            Calc.setExpression({id, hidden: true});
        }
    }
    func.desc = ["hide", arguments];
    return func;
}

// Instruction: show
// Parameter: ids - comma separated list of expression id's
// Shows (un-hides) all the expressions given as arguments to the instruction.
// Equivalent to set(id, {hidden: false}) for each of the given id's.
// Moves on to the next instruction immediately.
function show (...ids) {
    let verify = 1;
    const func = () => {
        if (verify) {
            verify = 0;
            for (let id of ids) {
                verifyId(id);
            }
        }
        for (let id of ids) {
            Calc.setExpression({id, hidden: false});
        }
    }
    func.desc = ["show", arguments];
    return func;
}

// Instruction: hideLabel
// parameter: ids - comma separated list of expression id's
// Turns off the label of all the expressions given as arguments to
// the instruction.  Equivalent to set(id, {showLabel: false}) for
// each of the given id's.  Moves on to the next instruction
// immediately.
function hideLabel (...ids) {
    let verify = 1;
    const func = () => {
        if (verify) {
            verify = 0;
            for (let id of ids) {
                verify(id);
            }
        }
        for (let id of ids) {
            Calc.setExpression({id, showLabel: false});
        }
    }
    func.desc = ["hideLabel", arguments];
    return func;
}

// Instruction: showLabel
// parameter: ids - comma separated list of expression id's
// Turns on the label of all the expressions given as arguments to
// the instruction.  Equivalent to set(id, {showLabel: true}) for
// each of the given id's.  Moves on to the next instruction
// immediately.
function showLabel (...ids) {
    let verify = 1;
    const func = () => {
        if (verify) {
            verify = 0;
            for (let id of ids) {
                verifyId(id);
            }
        }
        for (let id of ids) {
            Calc.setExpression({id, showLabel: true});
        }
    }
    func.desc = ["showLabel", arguments];
    return func;
}

// Instruction: setLabel
// Parameters: id - id of an expression with a label
//             labelStr - the desired label string
// Sets the label of the given expression to the given string.
// If the string uses latex, enclose the latex in back-ticks,
// as usual.
function setLabel (id, labelStr) {
    let verify = 1;
    const func = () => {
        if (verify) {
            verify = 0;
            verifyId(id);
        }
        Calc.setExpression({id, label: labelStr});
        return 0;
    }
    func.desc = ["setLabel", arguments];
    return func;
}

// Instruction: setValue
// Parameters: id - id of a "<name>=<value>" type of expression
//             value - latex string or number of new value
//             delay - number of ms to delay before next instruction
// Replaces the <value> part of the given expression with the given value.
// The value can be any latex expression string or a number.  If the
// expression has a slider that is playing, it will be stopped first.
function setValue (id, value, delay=0) {
    let verify = 1;
    const stop_slider = {id, type: 'set-slider-isplaying', isPlaying: 0};
    const func = () => {
        if (verify) {
            verify = 0;
            verifyId(id);
        }
        let name = Calc.getExpressions().filter(e => e.id === id.toString())[0].latex;
        name = name.slice(0, name.lastIndexOf("=") + 1);
        if (name[name.length - 1] != '=') {
            throw "expression does not contain '='";
        }
        const obj = { id, latex: name + value };
        Calc.controller.dispatch(stop_slider);
        Calc.setExpression(obj);
        return delay;
    }
    func.desc = ["setValue", arguments];
    return func;
}

// Instruction: startSlider
// Parameters: id - the id of an expression that has a slider
//             delay - number of ms to delay before next instruction
// Equivalent to pressing the play button on a slider when it is not
// yet running.
function startSlider (id, delay=0) {
    let verify = 1;
    const obj = {id, type: 'set-slider-isplaying', isPlaying: 1};
    const func = () => {
        if (verify) {
            verify = 0;
            verifyId(id);
        }
        Calc.controller.dispatch(obj);
        return delay;
    }
    func.desc = ["startSlider", arguments];
    return func;
}

// Instruction: stopSlider
// Parameters: id - the id of an expression that has a slider
//             delay - number of ms to delay before next instruction
// Equivalent to pressing the pause button on a slider when it is
// already running.
function stopSlider (id, delay=0) {
    let verify = 1;
    const obj = {id, type: 'set-slider-isplaying', isPlaying: 0};
    const func = () => {
        if (verify) {
            verify = 0;
            verifyId(id);
        }
        Calc.controller.dispatch(obj);
        return delay;
    }
    func.desc = ["stopSlider", arguments];
    return func;
}

// Instruction: animateValue
// Parmeters: id - the id of a "<name>=<value>" type of expression
//            startVal - the starting value for the animation
//            endVal - the ending value for the animation
//            interval - the amount to step by on each frame
//            frameTime - number of ms of explicit delay between frames
//            delay - number of ms to wait after animation is done
// Animates a variable by setting its value to startVal and incrementing or
// decrementing it by the given interval until it reaches endVal.  Speed
// can be controlled by changing the interval and by giving a frameTime value.
// This is similar to playing a slider, but allows explicit control over the
// speed and the step size, and allows running in reverse.  The instruction
// blocks until the endVal is reached, unlike startSlider which moves on to
// the next instruction after the slider starts.  If the expression has a
// slider that is playing, it will be stopped first.
function animateValue(id, startVal, endVal, interval, frameTime=0, delay=0) {
    let name;
    let stop_cond;
    let verify = 1;
    if (startVal == endVal) throw "Animate values equal";
    if (interval <= 0) throw "Bad interval parameter: " + interval;
    function animateHelper (val, incr) {
        if (stop_cond(val, endVal) || animating == 2) {
            const obj = { id, latex: name + endVal }
            Calc.setExpression(obj);
            animating = 0;
        } else {
            val += incr
            const obj = { id, latex: name + val.toFixed(5) };
            Calc.setExpression(obj);
            setTimeout(() => animateHelper(val, incr), frameTime);
        }
    }
    const stop_slider = {id, type: 'set-slider-isplaying', isPlaying: 0};
    const func = () => {
        if (verify) {
            verify = 0;
            verifyId(id);
        }
        Calc.controller.dispatch(stop_slider);
        name = Calc.getExpressions().filter(e => e.id === id.toString())[0].latex;
        name = name.slice(0, name.lastIndexOf("=")+1);
        if (name[name.length - 1] != '=') {
            throw "expression does not contain '='";
        }
        if (grouping) {
            // Running as a group, so go straight to the end value
            stop_cond = (val, endVal) => (true);
            animateHelper(endVal);
        } else if (startVal < endVal) {
            stop_cond = (val, endVal) => (val >= endVal);
            animating = 1;
            animateHelper(startVal, interval);
        } else {
            stop_cond = (val, endVal) => (val <= endVal);
            animating = 1;
            animateHelper(startVal, -interval);
        }
        return delay;
    }
    func.desc = ["animateValue", arguments];
    return func;
}

// Instruction: setSliderProperties
// Parmeters: id - the id of an expression with a slider
//            properties - the properties to be set
//            delay - number of ms to wait before next instruction
// Sets the given properties of the given slider.  The properties are:
//    min: <latex or number>
//    max: <latex or number>
//    step: <latex or number>
//    period: <time in ms from min to max>
//    loopMode: "LOOP_FORWARD_REVERSE" or
//              "LOOP_FORWARD" or
//              "PLAY_ONCE" or
//              "PLAY_FOREVER"
function setSliderProperties(id, properties, delay=0) {
    let verify = 1;
    const func = () => {
        if (verify) {
            verify = 0;
            verifyId(id);
        }
        if (properties.min !== undefined) {
            Calc.controller.dispatch({id, type: 'set-slider-minlatex', latex: properties.min.toString()});
        }
        if (properties.max !== undefined) {
            Calc.controller.dispatch({id, type: 'set-slider-maxlatex', latex: properties.max.toString()});
        }
        if (properties.step !== undefined) {
            Calc.controller.dispatch({id, type: 'set-slider-steplatex', latex: properties.step.toString()});
        }
        if (properties.period !== undefined) {
            Calc.controller.dispatch({id, type: 'set-slider-animationperiod', animationPeriod: properties.period});
        }
        if (properties.loopmode !== undefined) {
            Calc.controller.dispatch({id, type: 'set-slider-loopmode', loopMode: properties.loopmode});
        }
        return delay;
    }
    func.desc = ["setSliderLimits", arguments];
    return func;
}

// Instruction: set
// Parameter: id - id of an expression to operate on
//            properties - an object containing property/value pairs
//            delay - number of ms to delay before next instruction
// This is a generic instruction to set any property on the given expression.
// See the API documentation of Calculator.setExpression to see what can
// be set.  Example args parameter:  {label: "Hi", showLabel: true}.  This
// instruction can be used to create a new expression, if the given id does
// not currently exist and the 'latex' property is provided.
// Note: if using this to set the 'latex' property, this may not have any
// effect if the expression's slider is playing (even if it is set to "play once"
// and has reached the maximum value).  Use stopSlider beforehand, if necessary.
function set (id, properties, delay=0) {
    let verify = 1;
    const obj = { id, ...properties };
    const func = () => {
        if (verify) {
            verify = 0;
            const expr = Calc.getExpressions().filter(e => e.id === id.toString())[0];
            if (expr === undefined) {
                if (properties.latex === undefined) {
                    throw("set function with unknown id without latex property");
                }
            }
        }
        Calc.setExpression(obj);
        return delay;
    }
    func.desc = ["set", {1: id, 2: JSON.stringify(properties), 3: delay}];
    return func;
}

// Instruction: stop
// Parameter: message - message to display
// Causes the program to stop and display the given message string next to
// the Start/Stop button.  This gives the opportunity to do manual changes to
// the graph.  The message can give instructions on what to do.  The program
// will resume when the Start button is clicked.
function stop (messageStr) {
    const func = () => {
        message.innerHTML = messageStr;
        startButton.firstChild.innerHTML = 'Start';
        running = 0;
    }
    func.desc = ["stop", arguments];
    return func;
}

// Instruction: pause
// Parameter: delay - number of ms to pause
// This introduces a pause of the given duration into the program.  Although
// most instructions have a built-in ability to delay after running, some do not.
function pause (delay) {
    const func = () => delay;
    func.desc = ["pause", arguments];
    return func;
}

// Instruction: label
// Parameters: name - the name of this label
// Gives a name to the point in the instruction stream which
// can be the target of a goto instruction. Does not do anything
// functional.
function label (name) {
    const labelFunc = () => {
        // If called internally for filling in the labels object, add
        // this label to it.  Otherwise just return.
        if (labelIndex >= 0) {
            labels[name] = labelIndex;
        }
    }
    labelFunc.desc = ["label", arguments];
    return labelFunc;
}

// Instruction: goto
// Parameters: name - the name of the label to go to
//             repeat - the number of times to repeat
// Jumps to the specified label and decrements an internal count that
// is initialized to the repeat parameter.  If the internal count
// has reached zero, resets the count to the given repeat value, but
// does not jump to the given label.  This allows a set of instructions
// to be repeated the given number of times before moving on to the
// next instruction.  If another goto loops back to before this instruction,
// it will be ready to repeat again, allowing nested repeat loops to work.
// To repeat indefinitely, omit the repeat count parameter or set the
// repeat count to -1.
function goto (name, repeat=-1) {
    let count = repeat;
    let lastReset = 0;
    const gotoFunc = () => {
        if (grouping) {
            throw("\"goto\" not allowed in a statement group");
        }
        if (name in labels) {
            // If we have hit "reset" since we were last here,
            // reset the repeat count
            if (lastReset != resetCount) {
                count = repeat;
                lastReset = resetCount;
            }
            if (backStepping) {
                // Reset the count to what it was
                if (count == repeat) {
                    count = 0;
                } else {
                    count++;
                }
            } else {
                // Goto label if count>0, otherwise reset the count
                if (count == 0) {
                    count = repeat;
                } else {
                    count--;
                    currentIndex = labels[name];
                }
            }
        } else {
            disableButton(startButton);
            disableButton(stepButton);
            message.innerHTML = "Error: unknown label (\"" + name + "\")";
            throw("Unknown label: " + name);
        }
    }
    gotoFunc.desc = ["goto", arguments];
    return gotoFunc;
}

// --------------------------------
// Internal variables and functions
// --------------------------------

let Calc;
let currentIndex = -1;
let resetButton, startButton, message;
let stepButton, revStepButton, saveButton;
let running = 0, stepping = 0, grouping = 0, animating = 0, backStepping = 0;
let steps;
let labelIndex = -1;
let labels = {};
let debugMode = false;
let allowSave = false;
let history = [];

// Counter that increments when the reset button is
// pressed.  Used by the goto instruction to reset
// its internal count if a reset has occurred since
// it was last executed.
let resetCount = 0;

function testlog (s) {
    console.log(`%c${s}`, 'font-weight: bold; border: 1px solid black; border-radius: 999px; padding: 3px 5px 3px 5px');
}

function steplog (index, undo) {
    let dash = undo ? "-" : "";
    if (steps[index].constructor === Array) {
        let str = dash + (index + 1) + ": ";
        const indent = str.length;
        for (let i of steps[index]) {
            if (i != steps[index][0]) {
                str += " ".repeat(indent);
            }
            str += i.desc[0] + "(" + Object.values(i.desc[1]) + ")";
            if (i != steps[index][steps[index].length-1]) {
                str += "\n";
            }
        }
        testlog(str);
    } else {
        testlog(dash + (index + 1) + ": " + steps[index].desc[0] + "(" +
                    Object.values(steps[index].desc[1]) + ")");
    }
}

function enableButton (el) {
    if (el != undefined) {
        el.firstChild.classList.add('dcg-btn-green');
        el.firstChild.classList.remove('disabled-save-btn');
    }
}

function disableButton (el) {
    if (el != undefined) {
        el.firstChild.classList.remove('dcg-btn-green');
        el.firstChild.classList.add('disabled-save-btn');
    }
}

// Wait for animation to finish
function waitForAnimation (func, delay) {
    const interval = setInterval(() => {
        if (!animating) {
            clearInterval(interval);
            setTimeout(func, delay);
        }
    }, 100);
}

// Tell the animation to stop and then wait for it to do so
function cancelAnimation (func) {
    if (animating == 1) {
        // Special value of 2 tells animateHelper to stop now!
        animating = 2;
        waitForAnimation (func, 0);
    }
}

function advance () {
    setState(currentIndex + 1);
}

function runStatement(stmt) {
    let delay = 0;
    if (stmt.constructor === Array) {
        let saveGrouping = grouping;
        grouping = 1;
        for (let i of stmt) {
            runStatement(i);
        }
        grouping = saveGrouping;
    } else {
        delay = stmt();
    }
    if (running && !grouping) {
        if (animating) {
            waitForAnimation(advance, delay);
        } else {
            setTimeout(advance, delay);
        }
    }
}

function setState (index) {
    if (!running && !stepping) {
        return;
    }
    if (index >= steps.length) {
        running = 0;
        stepping = 0;
        startButton.firstChild.innerHTML = 'Start';
        markState(index);
        return;
    }
    index = Math.max(index, 0);
    currentIndex = index;
    steplog(index, false);
    markState(index);
    runStatement(steps[index]);
    if (!allowSave) {
        disableButton(saveButton);
    }
}

function markState (index) {
    if (index >= 0) {
        enableButton(resetButton);
        enableButton(revStepButton);
    } else {
        disableButton(resetButton);
        if (history.length == 0) {
            disableButton(revStepButton);
        }
    }
    if (index === steps.length) {
        disableButton(startButton);
        disableButton(stepButton);
    } else {
        enableButton(startButton);
        enableButton(stepButton);
    }
    message.innerHTML = (``);

    if (index >= 0 && index < steps.length && (debugMode || index == 0) && !backStepping) {
        history.push({i: index, state: Calc.getState()});
    }
}

function verifyId (id, desc) {
    const expr = Calc.getExpressions().filter(e => e.id === id.toString())[0];
    if (expr === undefined) {
        throw "undefined id (" + id + ")";
    }
}

// Set up the environment to run the given program
function desmosPlayer (program, properties={}) {

    const interval = setInterval(() => {
        if (document.querySelector('.save-button') && window.Calc) {
            Calc = window.Calc;
            init();
            clearInterval(interval);
        }
    }, 100);

    function init () {

        steps = program;

        let title = document.querySelector('.dcg-variable-title');

        // If a graphName is given, it has to match the graph title
        if ((properties.graphTitle != undefined) && (properties.graphTitle !== title.innerHTML)) {
            return;
        }

        if (properties.debugMode == true) {
            debugMode = true;
        }

        if (properties.allowSave == true) {
            allowSave = true;
        }

        testlog("desmosPlayer ready");

        saveButton = document.querySelector('.save-button');

        resetButton = saveButton.cloneNode(true);
        resetButton.firstChild.innerHTML = 'Reset';
        resetButton.addEventListener('click', () => {
            const func = () => {
                running = 0;
                currentIndex = -1;
                resetCount++;
                markState(-1);
                startButton.firstChild.innerHTML = 'Start';
                Calc.setState(history[0].state, { allowUndo: true });
                history = [];
            }
            if (animating) {
                cancelAnimation(func);
            } else {
                func();
            }
        })
        saveButton.after(resetButton);

        startButton = resetButton.cloneNode(true);
        startButton.firstChild.innerHTML = 'Start';
        startButton.addEventListener('click', () => {
            const func = () => {
                if (running) {
                    running = 0;
                    startButton.firstChild.innerHTML = 'Start';
                } else {
                    running = 1;
                    startButton.firstChild.innerHTML = 'Stop';
                    setState(currentIndex + 1);
                }
                stepping = 0;
            }
            if (animating) {
                cancelAnimation(func, 0);
            } else {
                func();
            }
        })
        resetButton.after(startButton);
        enableButton(startButton);

        stepButton = resetButton.cloneNode(true);
        stepButton.firstChild.innerHTML = 'Step';
        stepButton.addEventListener('click', () => {
            const func = () => {
                if (running) {
                    return;
                } else {
                    stepping = 1;
                    advance();
                    stepping = 0;
                }
            }
            if (animating) {
                cancelAnimation(func);
            } else {
                func();
            }
        })
        startButton.after(stepButton);
        enableButton(stepButton);

        if (debugMode) {
            revStepButton = resetButton.cloneNode(true);
            revStepButton.firstChild.innerHTML = 'Back Step';
            revStepButton.addEventListener('click', () => {
                const func = () => {
                    if (running) {
                        return;
                    } else if (currentIndex > -1) {
                        let lastState = history.pop();
                        currentIndex = lastState.i - 1;
                        Calc.setState(lastState.state);
                        steplog(lastState.i, true);
                        backStepping = 1;
                        if (steps[lastState.i].name == "gotoFunc") {
                            steps[lastState.i]();
                        }
                        markState(currentIndex);
                        backStepping = 0;
                    }
                }
                if (animating) {
                    cancelAnimation(func);
                } else {
                    func();
                }
            })
            stepButton.after(revStepButton);
        }

        message = title.cloneNode(true);
        message.style.maxWidth = '600px';

        const buttonContainer = document.querySelector('.save-btn-container');
        buttonContainer.after(message);
        buttonContainer.style.position = 'relative';
        buttonContainer.style.top = '-18px';

        document.querySelector('.align-center-container').style.display = 'none';

        // Fill in the label object with index values for each label
        for (labelIndex = 0; labelIndex < steps.length; labelIndex++) {
            if (steps[labelIndex].name == "labelFunc") {
                // The label name is known only to the function in the program
                // It will fill in labels[labelName] if global labelIndex >= 0.
                steps[labelIndex]();
            }
        }
        labelIndex = -1;

        const exprList = document.querySelector('.dcg-exppanel-outer');
        exprList.addEventListener('keydown', e => {
            if (e.code === 'KeyQ' && e.ctrlKey) {
                const selExprId = Calc.selectedExpressionId;
                if (selExprId == undefined) {
                    testlog("Select an expression");
                } else {
                    testlog("id: " + selExprId + " ("
                                + Calc.getExpressions().filter(e => e.id === selExprId.toString())[0].latex
                                + ")");
                }
            }
        })

        markState(currentIndex);
    }
}

Hello, the correct link to the original gist is https://gist.github.com/jared-hughes/b62dc3042947d6dcee16a186301227dc.

Fixed.