TableOfContent2Tree

const util = require('util');
let text =
    `#1
    ##1.1
        ###1.1.1
            ####1.1.1.1
            ####1.1.1.2
         ###1.1.2
            ####1.1.2.1
    ##1.2
          ###1.2.1
#2...`;
let rows = text.split('\n').map((x, i) => ({
    value: x.trimStart(),
    index: i
})).map(x => ({
    name: x.value.match(/(?<=#+)[^#]+/)[0],
    level: x.value.match(/#*(?=[^#])/)[0].length,
    index: x.index
}));
rows.forEach(x=> x.parent_id=rows.filter(y=> y.index<x.index && y.level<x.level).pop()?.index);
console.log('Размеченный список оглавления:', rows);
let tree = {};
const makeTree = (nodes, parentId) => {
    return nodes
        .filter((node) => node.parent_id === parentId)
        .reduce(
            (tree, node) => [
                ...tree,
                {
                    ...node,
                    children: makeTree(nodes, node.index),
                },
            ],
            [],
        )
};
tree = makeTree(rows,undefined);
console.log("Дерево: ",util.inspect(tree,false,10,true));