w3c-xml-validator

A Node.js library for programmatically confirming whether a given XML document is both well-formed and valid according to the specified DTD.

Why?

I was frustrated by the lack of programmatic options for validating XML with JavaScript...in particular, when validating against a public DTD, and without requiring something like libxml to be installed locally.

There are one or two other modules that come close, but they either don't meet those requirements, or aren't cross-platform. This one is!

W3C

This library relies on the online validator provided by W3C. Please consider donating to the W3C if you find this library useful, because without their tools, this one wouldn't exist. Click on the logo below:

Programmatic Use

This module exports a function that accepts a single value: the XML to be validated. The XML must contain a !DOCTYPE element that refers to a publicly-accessible DTD. The return value is a Promise that will be fulfilled or rejected with the values described below.

Example:

const validate = require('w3c-xml-validator')
const xml = '<?xml version="1.0" encoding="utf-8"?>...' // note: this can be a {String} value or a {Buffer}

validate(xml)
    .then(function (response) {
        // the response will contain a basic is/is not valid flag, plus warnings and errors (if present)
    })
    .catch(function (err) {
        // the promise may be rejected for any of the reasons listed below
    })

Fulfillment

When the promise is fulfilled, the returned value will be a plain object with the following properties:

Key	Data type	Notes
doctype	{String}	The DTD that the validator used.
isValid	{Boolean}	A simple yes/no based on the results from the W3C validation tool.
warnings	{Array} of {String}	This is a list of the entries under "Notes and Potential Issues". Each value is the entry title, not the verbose description.
errors	{Array} of {String}	This is a list of the entries under "Validation Output: # Error(s)". Each value is the entry title that appears in bold, not the verbose description.

isValid will have the same value as (errors.length === 0). warnings may have entries, even if the validation is successful.

Rejection

The promise may be rejected for any of the following reasons:

• The input parameter is undefined, null, or an empty string.
• The input parameter is not markup (meaning, not XML or HTML or anything else that the validator cannot parse). In this case, there will be an error message The remote server replied with a 307 status code. (Personally, I think it should really be a 400 code, but 🤷)
• The W3C web site is not reachable.
• The HTTP response code is something other than 200.

Check the message property of the error object to find out more information about the source of the problem. If you feel there is an issue with the code in this project, please submit a ticket on GitHub for help.

Command Line Use

This library can also be called from the command line. The XML to validate can either be piped into the library:

(Linux or macOS)

$ cat file-to-validate.xml | npx w3c-xml-validator

(Windows)

PS> type file-to-validate.xml | npx w3c-xml-validator

or the file name provided as an argument:

(Linux/Windows/macOS)

$ npx w3c-xml-validator file-to-validate.xml

The exit code will be non-zero if isValid === false. Any rejections will be output to stderr.

License

Please refer to LICENSE.