With your solution i get an error Unexpected token � in JSON at position 0...

const jsonStrOriginalValue = JSON.stringify(secondRenderJsonData)
const value = btoa(jsonStrOriginalValue) //unescape(encodeURIComponent()) //Buffer.from(jsonStrOriginalValue).toString('base64') 

document.getElementsByTagName('body')[0].innerHTML += `<span class='jsreport-pdf-utils-page-item jsreport-pdf-utils-hidden-element' style='font-family: Helvetica;position:absolute;text-transform: none;opacity: 0.01;font-size:1.1px'>item@@@${value}@@@</span>`

Error when evaluating custom script /main.js
Unexpected token � in JSON at position 0

(sandbox.js line 33:19)

  31 |     }
  32 |
> 33 |     const $pdf  = await jsreport.pdfUtils.parse(res.content, true)
     |                   ^
  34 |     let page = $pdf.pages[$pdf.pages.length]
  35 |     let jsonData = []
  36 |     

SyntaxError: Unexpected token � in JSON at position 0

What is the meaning of the notation item@@@...@@@?
Is this somehow processed differently?

If I use itemm@@...@@@ or something else, it works. But the base64 string (content between @@@...@@@) gets clipped when I try to get it via regex, probably it gets clipped at the page margin.

But in the inline script to parse the DOM i can't use new Buffer.from(title, 'utf8').toString('base64'). I can only use atob/btoa there.

Base64 is not the best solution, at least not for utf8. Some special characters are not encoded correctly.

So I just replace the spaces with the html equivalent title.replace(/ /gi, ' ').

And with a very long TOC in the attached code tag, which contains the headers as JSON code, split by a page break, the readout in the afterRender via regex no longer works. So I tried to minimize the font size.

code.setAttribute('style', 'font-size: 0.05px;')

What is the smallest font size that is rendered?

Ok, I tried it and found it to be excellent.

https://playground.jsreport.net/w/fhrtms/WDA4w4ao

But i found a little bug with spaces:

It is always the last space of innerHTML property.

This could look pretty interesting. And I might have an interface to exchange data between the two renderings.

On the first render i run an inline script at the end of DOM, and put a pseudo handlebar at the end of body:

toc = [{items: []}]
const regex = /<h([1-6]).*>(.*)<\/h\1>/g;

const str = document.getElementsByTagName('body')[0].innerHTML;
let m;
let tocItems = []

while((m = regex.exec(str)) !== null) {
    
    if(m.index === regex.lastIndex) {
        regex.lastIndex++;
    }

    let div = document.createElement('div');
    div.innerHTML = m[0].trim();

    let header = {
        title: div.firstChild.innerHTML,
        id: div.firstChild.id,
        parent: div.firstChild.getAttribute('data-parent') || null,
    }

    toc[0].items.push(header)
    tocItems.push(header)

    m.forEach((match, groupIndex) => {
        console.log(`Found match, group ${groupIndex}: ${match}`);
    });
}

let secondRenderJsonData = []

// PARSE STUCTURE
toc.forEach((page, pIndex, arr)=> {

    page.items.forEach((item, iIndex, arr)=> {
        
        if(item.title) {
            secondRenderJsonData.push({id: item.id, title: item.title, parent: item.parent || null, page: pIndex + 1})
        }
    })
})

var code = document.createElement('code')
code.setAttribute('ref', 'toc')
code.innerHTML = '{' + '{#secondRenderJsonData}}' + JSON.stringify(secondRenderJsonData) + '{' + '{/secondRenderJsonData}}'
console.log('code', code.outerHTML)
document.getElementsByTagName('body')[0].appendChild(code);

Then i use your second rendering approach, with filtering the pseudo handlebar and pass it as parsed json data to the second rendering:

async function afterRender (req, res) {
    if (req.data.secondRender) {
        return
    }

    const $pdf  = await jsreport.pdfUtils.parse(res.content, true)
    let page = $pdf.pages[$pdf.pages.length]
    let jsonData = []
    
    for(var i=0; i <= $pdf.pages.length; i++) {
        let page = $pdf.pages[i]
        //console.log('parsedResult', page)

        if(page && page.text) {
            const regex = /{{#secondRenderJsonData}}(.*){{\/secondRenderJsonData}}/gm;
            let m;

            while ((m = regex.exec(page.text)) !== null) {
                
                if (m.index === regex.lastIndex) {
                    regex.lastIndex++;
                }

                if(m[1]) {
                    jsonData = m[1]
                }
            }
        }
    }
            
    //console.log('jsonData: ', jsonData);

    const finalR = await jsreport.render({
        template: {
            name: 'template',
        },
        data: {
            ...req.data,
            $pdf: $pdf,
            firstRenderPdf: $pdf,
            secondRender: true,
            secondRenderTOC: (typeof jsonData === 'string') ? JSON.parse(jsonData) : jsonData,
        }
    })
    res.content = finalR.content
}

And then i write the links dynamically with the #each loop handlebar syntax:

{{#each secondRenderTOC}}
    <a class="block" 
        title="{{this.title}}" 
        href="#{{this.id}}" 
        data-pdf-link-target-id="{{this.id}}" 
        data-pdf-outline 
        data-pdf-outline-title="{{this.title}}" 
        data-pdf-outline-parent="{{this.parent}}"
    >
        <div class="relative w-full">
            <span class="chapter w-full block">{{this.title}}</span>
            <strong class="page absolute top-0 right-0 pl-2 bg-white">{{getPageNumber this.id}}</strong>
        </div>
    </a>
{{/each}}

Here my fork of your solution: https://playground.jsreport.net/w/fhrtms/z9GUrD79

I'll test it again in a more complex structure.

It not works very well. I mixed the stuff for testing reasons in my test environment in a non linear way.

I really hate to bug you guys, but I find this topic kind of exciting. I would like to get the TOC somehow dynamic. The most suitable way is to read the header directly from DOM, preferably without additional function calls in the html source code. Can i call the pdfAddPageItem function directly via script from my template? Or can deal with the rendered dom in the script section (under the html sourcecode)?

So, I want to parse the finished DOM outside the template and pass the found elements to the function pdfAddPageItem purely script based (not via handlebars). But somehow I can't get to the html source of the finished DOM.

The HMTL DOM is correct. The remixed order in the DOM looks like this:

1. Heading (main)
1.1. Heading (main)
        3. Heading (child)
        3.1. Heading (child)
        3.2. Heading (child)
                4. Heading (child-child)
                4.1. Heading (child-child)
                5. Heading (child-child)
                5.1. Heading (child-child)
                5.1.1. Heading (child-child)
                5.2. Heading (child-child)
1.1.1. Heading (main)
1.2. Heading (main)
1.2.1. Heading (main)
2. Heading (main)
2.1. Heading (main)
2.2. Heading (main)
2.3. Heading (main)
        3. Heading (child)
        3.1. Heading (child)
        3.2. Heading (child)
                4. Heading (child-child)
                4.1. Heading (child-child)
                5. Heading (child-child)
                5.1. Heading (child-child)
                5.1.1. Heading (child-child)
                5.2. Heading (child-child)

With a little hassle I get the pdf TOC mapped with the function pdfAddPageItem and my little helper function pdfAddTocItem.

Yes ok that looks a bit weird:

"laterToc": [
  { "title": "1. Heading", "parent": "root", "id": "h-1" },
  { "title": "1.1. Heading", "parent": "h-1", "id": "h-1-1" },
  { "title": "1.1.1. Heading", "parent": "h-1-1", "id": "h-1-1-1" },
  { "title": "1.2. Heading", "parent": "h-1", "id": "h-1-2" },
  { "title": "1.2.1. Heading", "parent": "h-1-2", "id": "h-1-2-1" },
  { "title": "2. Heading", "parent": "root", "id": "h-2" },
  { "title": "2.1. Heading", "parent": "h-2", "id": "h-2-1" },
  { "title": "2.2. Heading", "parent": "h-2", "id": "h-2-2" },
  { "title": "2.3. Heading", "parent": "h-2", "id": "h-2-3" },
  { "title": "3. Heading", "parent": "h-1-1", "id": "noh-3" },
  { "title": "3.1. Heading", "parent": "noh-3", "id": "nonoh-3" },
  { "title": "3.2. Heading", "parent": "noh-3", "id": "noh-3-2" },
  { "title": "3. Heading", "parent": "root", "id": "yesh-3" },
  { "title": "3.1. Heading", "parent": "yesh-3", "id": "yesyesh-3" },
  { "title": "3.2. Heading", "parent": "yesh-3", "id": "yesh-3-2" },
  { "title": "4. Heading", "parent": "h-1-1", "id": "abcnoh-4" },
  { "title": "4.1. Heading", "parent": "abcnoh-4", "id": "abcnoh-4-1" },
  { "title": "5. Heading", "parent": "h-1-1", "id": "abcnoh-5" },
  { "title": "5.1. Heading", "parent": "abcnoh-5", "id": "abcnoh-5-1" },
  { "title": "5.1.1. Heading", "parent": "abcnoh-5-1", "id": "abcnoh-5-1-1" },
  { "title": "5.2. Heading", "parent": "abcnoh-5", "id": "abcnoh-5-2" },
  { "title": "4. Heading", "parent": "root", "id": "abcyesh-4" },
  { "title": "4.1. Heading", "parent": "abcyesh-4", "id": "abcyesh-4-1" },
  { "title": "5. Heading", "parent": "root", "id": "abcyesh-5" },
  { "title": "5.1. Heading", "parent": "abcyesh-5", "id": "abcyesh-5-1" },
  { "title": "5.1.1. Heading","parent": "abcyesh-5-1","id": "abcyesh-5-1-1"},
  { "title": "5.2. Heading", "parent": "abcyesh-5", "id": "abcyesh-5-2" }
]

Or should I make the work and try to program a possible extension on nodejs level?

Hmm, I don't think that's enough. I don't get all elements when I run it at the top of the page. At the end of the page it works fine.

I haven't really figured out the asynchronous functions yet 🤷

// THIS NOT WORKING
async function laterToc(data) {
    //console.log('data', new Date, data.data.root.toc)
    
    await jsreport.templatingEngines.waitForAsyncHelpers()
    
    return new Promise((resolve) => {   
        //console.log('resolve', new Date, data, resolve)
        
        let res = ()=> {
            //console.log('res', new Date, data)
            let result = []

            data.data.root.toc.forEach((item, iIndex, arr)=> {
                if(item && item.title && item.id) {
                    result.push(`<a class="block" href="#${item.id}" data-pdf-link-target-id="${item.id}" data-pdf-outline data-pdf-outline-title="${item.title}" data-pdf-outline-parent="${item.parent}">${item.title}</a>`)
                }
            })

            //console.log('resolve-result', result.join("\n"))
    
            return result.join("\n");
        }

        resolve(res())
    })
}

YES, your tip with the delayed handlebar in combination with the main template was the right one ... https://playground.jsreport.net/w/fhrtms/Oxr_HbAT

I have now messed it up so that it works.

Many many thanks to @jan_blaha!

So here's what I have:

• multiple nested templates with many headings and registering via {{pdfAddPageItem...
• a TOC template that I merge (multiple if you like) at the end or/and start of the final pdf
• root TOC element <a href="#root" data-pdf-link-target-id="root" data-pdf-outline data-pdf-outline-title="My little document"></a>{{pdfAddPageItem "root"}}
• the delayed function with {{laterToc...}}

I just have to play with the delay and increase it a bit depending on the workload.

i am still working on a solution to place the TOC in any position

When I want to build the pdf TOC from a handlebar loop, it does not work. The static one does.

<!-- THIS WORKS -->
<a title="Root" href="#root" class="hidden" 
   data-pdf-link-target-id="root" 
   data-pdf-outline 
   data-pdf-outline-title="My little document"
>My little document</a>

<!-- THIS DOESN'T WORK-->
{{#each @root.$pdf.pages as | page |}}
    {{#each this.items as | item |}}
        {{#if this.id}}
            <a title="{{this.title}}" href="#{{this.id}}" 
               data-pdf-link-target-id="{{this.id}}" 
               data-pdf-outline 
               data-pdf-outline-title="{{this.title}}" 
               data-pdf-outline-parent="{{this.parent}}"
            >{{this.title}} ... {{increment @../index}}</a>
        {{/if}}
    {{/each}}
{{/each}}

When i watch/log the result in @jsreport/jsreport-pdf-utils/lib/worker.js at the end of reporter.afterTemplatingEnginesExecutedListeners.add i see that the HTML content is correct.

The output of req.context.pdfUtilsOutlines also seems correct.