How to Convert XML to JSON in JavaScript and Python

<order id="ord_1">
  <customer>Ana</customer>
  <zip>007</zip>
  <items>
    <item><sku>A-1</sku><qty>2</qty></item>
  </items>
</order>

import { XMLParser } from "fast-xml-parser";

new XMLParser().parse(xml);
// {"order":{"customer":"Ana","zip":7,"items":{"item":{"sku":"A-1","qty":2}}}}

• The id attribute is gone. fast-xml-parser ignores attributes unless told otherwise.
• zip became the number 7. Numeric-looking text is converted, and the leading zeros are lost.
• item is an object. Add a second <item> and the same path becomes an array, so code that reads items.item.sku works for one order and breaks for the next.

const parser = new XMLParser({
  ignoreAttributes: false,
  attributeNamePrefix: "@",
  parseTagValue: false,
  isArray: (name, jpath) => jpath === "order.items.item",
});

parser.parse(xml);
// {"order":{"customer":"Ana","zip":"007","items":{"item":[{"sku":"A-1","qty":"2"}]},"@id":"ord_1"}}

• ignoreAttributes: false keeps attributes, and attributeNamePrefix: "@" marks them, so @id cannot clash with a child element named id.
• parseTagValue: false keeps every value as a string. Convert numbers yourself, for the fields you know are numeric.
• isArray forces the listed paths to always be arrays, whether the document has one item or many. List every repeating element of your format here.

Python's standard library parses XML with ElementTree. A short function turns the tree into dictionaries, prefixing attributes with @:

import xml.etree.ElementTree as ET

def to_dict(element, list_tags=()):
    children = list(element)
    if not children and not element.attrib:
        return element.text
    result = {"@" + key: value for key, value in element.attrib.items()}
    for child in children:
        value = to_dict(child, list_tags)
        if child.tag in list_tags:
            result.setdefault(child.tag, []).append(value)
        elif child.tag in result:
            if not isinstance(result[child.tag], list):
                result[child.tag] = [result[child.tag]]
            result[child.tag].append(value)
        else:
            result[child.tag] = value
    return result

to_dict(ET.fromstring(xml), list_tags={"item"})
# {'@id': 'ord_1', 'customer': 'Ana', 'zip': '007', 'items': {'item': [{'sku': 'A-1', 'qty': '2'}]}}

ElementTree keeps text as strings, so 007 survives. The list_tags argument does the same job as isArray: without it, one <item> becomes a dictionary and two become a list.

XML has features that JSON does not, such as entity declarations, and some of them can be abused. Python's documentation warns that its XML modules are not secure against maliciously constructed data and recommends the defusedxml package for untrusted input. In Node, keep fast-xml-parser's entity options at their defaults unless you know you need more, and limit the size of the documents you accept.