[ExtendScript] Get bounds of selected text

I added to Mark's code 1) the exact color for the rectangle instead of the unpredictable swatch index, 2) get selected text layer to create the rectangle, and 3) the isSelectRect boolean key to select the rectangle after the script runs.

/**
 * Draw rectangle showing selected text's bounds.
 *  m1b
 * @discussion https://community.adobe.com/t5/illustrator-discussions/how-to-draw-a-graphic-on-hidden-character-in-illustrator/m-p/13833618
 */
(function () {

    var isSelectRect = true,
        doc = app.activeDocument,
        text = doc.selection,
        bounds = getTextOutlineBounds(text);

    if (bounds == undefined) {
        alert('Could not calculate bounds. Please select some text and try again.');
        return;
    }

    var rectColor = new CMYKColor();
    rectColor.cyan   = 0;
    rectColor.magenta = 100;
    rectColor.yellow = 100;
    rectColor.black  = 0;
    var lay = (text.typename == 'TextRange') ? text.parent.textFrames[0].layer : text[0].layer;

    // draw a rectangle just for showing the bounds
    var rect = lay.pathItems.rectangle(bounds[1], bounds[0], bounds[2] - bounds[0], -(bounds[3] - bounds[1])); // TLWH
    rect.fillColor = rectColor;
    rect.opacity = 30;
    // reset text selection requires CS6 or CC
    if (parseInt(app.version) >= 16 && isSelectRect) {
      app.executeMenuCommand('deselectall');
      rect.selected = true;
    }
})();


/**
 * Returns bounds of Text object [L, T, R, B].
 *  m1b
 *  2023-06-02
 *  {Text|Paragraph|Line|Word|Character} text - an Indesign text object.
 *  {Array<Number>} - the bounds [T, L, B, R].
 */
function getTextOutlineBounds(text) {

    var bounds;

    if (text.constructor.name == 'Array') {

        // process each element of array
        for (var i = 0; i < text.length; i++)
            bounds = expandBoundsForIllustrator(bounds, getTextOutlineBounds(text[i]));

        return bounds;

    }

    else if (text.constructor.name == 'TextFrame') {
        // process the text of the text frame
        return getTextOutlineBounds(text.textRange);
    }

    else if (
        !text.hasOwnProperty('characters')
        || text.characters.length == 0
        || !text.hasOwnProperty('fillColor')
    )
        // can't work with this
        return;

    var tf = text.parent.textFrames[0],
        arbitraryValue = 61.803;

    // we'll paint the text with this
    // color so that when it's outlined,
    // we can differentiate it
    var markerColor = new CMYKColor();
    markerColor.cyan = arbitraryValue;
    markerColor.magenta = arbitraryValue;
    markerColor.yellow = arbitraryValue;
    markerColor.black = arbitraryValue;

    var dup = tf.duplicate(),
        start = text.start,
        end = text.end;

    // mark the selected characters
    for (var i = start; i < end; i++)
        dup.characters[i].fillColor = markerColor;

    // a stringified version for matching purposes
    var matchMarker = stringify(dup.characters[start].fillColor);

    // the outlines are always compoundPathItems
    var outlines = dup.createOutline().compoundPathItems;

    // find the marked outlines
    for (var i = 0; i < outlines.length; i++)
        if (stringify(outlines[i].pathItems[0].fillColor) == matchMarker)
            bounds = expandBoundsForIllustrator(bounds, outlines[i].visibleBounds);

    // delete temporary items
    for (var i = outlines.length - 1; i >= 0; i--)
        outlines[i].remove();

    return bounds;

};


/**
 * Returns bounds that encompass both bounds.
 *  m1b
 *  2022-07-24
 *  {Array} b1 - bounds array [l, t, r, b].
 *  {Array} b2 - bounds array [l, t, r, b].
 *  {Array} - the encompassing bounds.
 */
function expandBoundsForIllustrator(b1, b2) {

    if (!b1 && !b2)
        return;

    if (!b1 && b2)
        return b2.slice();

    if (!b2 && b1)
        return b1.slice();

    var expanded = b2.slice();

    for (var i = 0; i < 4; i++) {
        if (b1[i] != undefined && b2[i] == undefined) expanded[i] = b1[i];
        if (b1[i] == undefined && b2[i] != undefined) expanded[i] = b2[i];
        if (b1[i] == undefined && b2[i] == undefined) return;
    }

    if (b1[0] < b2[0]) expanded[0] = b1[0];
    if (b1[1] > b2[1]) expanded[1] = b1[1];
    if (b1[2] > b2[2]) expanded[2] = b1[2];
    if (b1[3] < b2[3]) expanded[3] = b1[3];

    return expanded;

};


/**
 * Stringify tailored for the purpose
 * of identifying identical Swatches.
 *  m1b
 *  2023-04-26
 *  {Object} obj - the object to stringify.
 *  {String}
 */
function stringify(obj) {

    var str = obj.toString();

    for (var key in obj) {

        if (!obj.hasOwnProperty(key))
            continue;

        if (
            key == 'spot'
            || key == 'color'
        )
            str += stringify(obj[key]);

        else
            str += (obj[key]);

    }

    return str;

};