gistfile1.js

var categoryExport = ``;

var lineRx = /^(\t*)(\d+) (.+)$/;
var toSlug = function(label) {
	return String(label).replace('&', 'und').replace(/[^a-z0-9]/ig, '-');
};

var toCategoryObject = function(category) {
	category = lineRx.exec(category);
	return {
		level: category[1].length,
		id: +category[2],
		label: category[3],
		slug: toSlug(category[3])
	};
};

var addParentId = function() {
	var previous = { level: -1 };
	var levels = [];
	return function(category) {
		var array;

		if(category.level > previous.level) {
			array = [];
			levels.push(array);
		} else {
			array = levels[category.level];
			levels.length = category.level + 1;
		}

		array.push(category);
		category.parentId = ((levels[levels.length - 2] || []).slice(-1)[0] || {}).id || 0;
		previous = category;
	};
};

var categories = categoryExport.split('\n');

categories = categories.map(toCategoryObject);
categories.forEach(addParentId());

JSON.stringify(categories, 2, '  ');