Inquiry on Native/In-built Support for Converting IDML to JSON

I don’t normally work in this area, but I wanted to share something that might give you a starting point. This was originally built for Illustrator, so some pieces might not directly translate to InDesign, but the overall structure could be useful.

I cobbled this together from a few sources:

• A JSON polyfill I found on GitHub

• Some bits of functionality from other scripts I found online

• A few pieces I added with ChatGPT’s help cos I have no idea what I'm doing here - honesty is the best policy

It’s definitely not a finished or “best practice” version, but it does export document structure (artboards > layers > paths) to JSON.

Hopefully, this gives you something to work from or adapt for InDesign scripting.

The scripting gurus are better versed in this stuff than I am. But every little helps, or maybe in this case it doesn't.

/* ============================
   JSON POLYFILL FOR ILLUSTRATOR
   ============================ */

if (typeof JSON !== "object") {
    JSON = {};
}

(function () {
    "use strict";

    function f(n) {
        return n < 10 ? "0" + n : n;
    }

    if (typeof Date.prototype.toJSON !== "function") {
        Date.prototype.toJSON = function () {
            return isFinite(this.valueOf())
                ? this.getUTCFullYear() + "-" +
                  f(this.getUTCMonth() + 1) + "-" +
                  f(this.getUTCDate()) + "T" +
                  f(this.getUTCHours()) + ":" +
                  f(this.getUTCMinutes()) + ":" +
                  f(this.getUTCSeconds()) + "Z"
                : null;
        };
        String.prototype.toJSON =
        Number.prototype.toJSON =
        Boolean.prototype.toJSON = function () {
            return this.valueOf();
        };
    }

    var cx,
        escapable = /[\\\"\u0000-\u001f\u007f-\u009f]/g,
        gap,
        indent,
        meta = {    // table of character substitutions
            "\b": "\\b",
            "\t": "\\t",
            "\n": "\\n",
            "\f": "\\f",
            "\r": "\\r",
            "\"": "\\\"",
            "\\": "\\\\"
        },
        rep;

    function quote(string) {
        escapable.lastIndex = 0;
        return escapable.test(string)
            ? "\"" + string.replace(escapable, function (a) {
                  var c = meta[a];
                  return typeof c === "string"
                      ? c
                      : "\\u" + ("0000" + a.charCodeAt(0).toString(16)).slice(-4);
              }) + "\""
            : "\"" + string + "\"";
    }

    function str(key, holder) {
        var i,
            k,
            v,
            length,
            mind = gap,
            partial,
            value = holder[key];

        if (
            value &&
            typeof value === "object" &&
            typeof value.toJSON === "function"
        ) {
            value = value.toJSON(key);
        }

        if (typeof rep === "function") {
            value = rep.call(holder, key, value);
        }

        switch (typeof value) {
            case "string":
                return quote(value);

            case "number":
                return isFinite(value) ? String(value) : "null";

            case "boolean":
            case "null":
                return String(value);

            case "object":
                if (!value) {
                    return "null";
                }

                gap += indent;
                partial = [];

                if (Object.prototype.toString.apply(value) === "[object Array]") {
                    length = value.length;
                    for (i = 0; i < length; i += 1) {
                        partial[i] = str(i, value) || "null";
                    }

                    v =
                        partial.length === 0
                            ? "[]"
                            : gap
                            ? "[\n" +
                              gap +
                              partial.join(",\n" + gap) +
                              "\n" +
                              mind +
                              "]"
                            : "[" + partial.join(",") + "]";
                    gap = mind;
                    return v;
                }

                if (rep && typeof rep === "object") {
                    length = rep.length;
                    for (i = 0; i < length; i += 1) {
                        if (typeof rep[i] === "string") {
                            k = rep[i];
                            v = str(k, value);
                            if (v) {
                                partial.push(quote(k) + ":" + v);
                            }
                        }
                    }
                } else {
                    for (k in value) {
                        if (Object.prototype.hasOwnProperty.call(value, k)) {
                            v = str(k, value);
                            if (typeof v !== "undefined") {
                                partial.push(quote(k) + ":" + v);
                            }
                        }
                    }
                }

                v =
                    partial.length === 0
                        ? "{}"
                        : gap
                        ? "{\n" +
                          gap +
                          partial.join(",\n" + gap) +
                          "\n" +
                          mind +
                          "}"
                        : "{" + partial.join(",") + "}";
                gap = mind;
                return v;
        }
    }

    if (typeof JSON.stringify !== "function") {
        JSON.stringify = function (value, replacer, space) {
            var i;
            gap = "";
            indent = "";

            if (typeof space === "number") {
                for (i = 0; i < space; i += 1) {
                    indent += " ";
                }
            } else if (typeof space === "string") {
                indent = space;
            }

            rep = replacer;

            if (
                replacer &&
                typeof replacer !== "function" &&
                (typeof replacer !== "object" ||
                    typeof replacer.length !== "number")
            ) {
                throw new Error("JSON.stringify");
            }

            return str("", { "": value });
        };
    }
})();

/* ============================
   ILLUSTRATOR EXPORT SCRIPT (GENERIC)
   ============================ */

function exportToJSON() {
    if (app.documents.length === 0) {
        alert("No document open");
        return;
    }

    var doc = app.activeDocument;

    var jsonData = {
        documentName: "document_name",
        artboards: [],
        layers: []
    };

    // Artboards
    for (var i = 0; i < doc.artboards.length; i++) {
        var ab = doc.artboards[i];
        jsonData.artboards.push({
            name: "Artboard " + (i + 1),
            rect: ab.artboardRect
        });
    }

    // Layers
    for (var j = 0; j < doc.layers.length; j++) {
        var layer = doc.layers[j];
        var layerData = {
            name: "Layer " + (j + 1),
            visible: layer.visible,
            locked: layer.locked,
            paths: []
        };

        // Paths
        for (var k = 0; k < layer.pathItems.length; k++) {
            var p = layer.pathItems[k];
            layerData.paths.push({
                name: "Path " + (k + 1),
                closed: p.closed,
                points: p.pathPoints.length
            });
        }

        jsonData.layers.push(layerData);
    }

    var jsonString = JSON.stringify(jsonData, null, 2);

    var file = new File(Folder.desktop + "/illustrator_export.json");
    file.open("w");
    file.write(jsonString);
    file.close();

    alert("Export complete. File saved to Desktop.");
}

exportToJSON();

Afaik their is no official documentation or sample to convert IDML to JSON. You will have to understand the IDML schema and then write the convertor yourself. As mentioned by @Peter Kahrel, IDML is a bunch of XML files so XML parsing would be your friend.

-Manan

An IDML file is in fact a zipped collection of XML files. You cannot therefore convert an IDML file to JSON, you'll have to unpack the IDML, then convert each constituent XML file. Whether there's a documented usecase for converting an IDML's XML files to JSON I've no idea.