mso-conditional-parser

Parser and translator for MSO (Outlook) conditional comments in HTML email.

Parses all real-world MSO comment patterns, validates conditions against known Outlook versions and operators, and translates them into human-readable English.

Used as the core engine by eslint-plugin-mso-email and the MSO Conditional Comments VS Code extension.

Installation

npm install mso-conditional-parser

Requires Node.js 18+. ES module only ("type": "module").

API

parseMsoComment(str)

Parses an MSO conditional comment opener.

Returns a result object or null if the input is not a recognised MSO opener.

import { parseMsoComment } from 'mso-conditional-parser';

parseMsoComment('<!--[if gte mso 16]>');
// {
//   type: 'downlevel-hidden',
//   condition: 'gte mso 16',
//   translation: 'Outlook 2016, 2019, and 365 and newer',
//   isValid: true
// }

parseMsoComment('<!--[if mos]>');
// {
//   type: 'downlevel-hidden',
//   condition: 'mos',
//   translation: 'mos',
//   isValid: false,
//   error: "Use the keyword 'mso', not 'mos'",
//   conditionFix: 'mso'
// }

Supported opener patterns:

| Pattern | Type | |---|---| | <!--[if mso]> | downlevel-hidden | | <!--[if gte mso 16]> | downlevel-hidden | | <!--[if !mso]><!-- | downlevel-revealed | | <![if !mso]> | downlevel-revealed (non-standard) |

Result shape:

| Field | Type | Description | |---|---|---| | type | string | 'downlevel-hidden' or 'downlevel-revealed' | | condition | string | Raw condition string extracted from the comment | | translation | string | Human-readable English translation | | isValid | boolean | true if the condition is syntactically valid | | error | string | Present when isValid is false | | conditionFix | string | Optional replacement condition when a safe autofix exists |

validateCondition(condition)

Returns an error message for an invalid condition string, or null when valid.

import { validateCondition } from 'mso-conditional-parser';

validateCondition('mos'); // "Use the keyword 'mso', not 'mos'"
validateCondition('gte mso 16'); // null

getConditionFix(condition)

Returns a replacement condition string when a deterministic fix exists (for example mos → mso), or null otherwise.

import { getConditionFix } from 'mso-conditional-parser';

getConditionFix('mos'); // 'mso'
getConditionFix('gte mso 16'); // null

parseMsoEndComment(str)

Parses an MSO conditional comment closer.

Returns { type, isClosing: true } or null if not recognised.

import { parseMsoEndComment } from 'mso-conditional-parser';

parseMsoEndComment('<![endif]-->');
// { type: 'downlevel-hidden-end', isClosing: true }

parseMsoEndComment('<![endif]>');
// { type: 'downlevel-revealed-end', isClosing: true }

translateCondition(condition)

Translates a raw condition string into English without full parsing.

import { translateCondition } from 'mso-conditional-parser';

translateCondition('gte mso 16');  // 'Outlook 2016, 2019, and 365 and newer'
translateCondition('!mso');        // 'non-Outlook email clients'
translateCondition('mso 12');      // 'Outlook 2007'

isMsoComment(str)

Returns true if the string is any MSO comment — opener or closer.

import { isMsoComment } from 'mso-conditional-parser';

isMsoComment('<!--[if mso]>');   // true
isMsoComment('<![endif]-->');    // true
isMsoComment('<p>hello</p>');    // false

Supported conditions

| Syntax | Example | Meaning | |---|---|---| | mso | <!--[if mso]> | Any Outlook version | | !mso | <!--[if !mso]><!-- | Non-Outlook clients | | mso <version> | <!--[if mso 16]> | Exact Outlook version | | <op> mso <version> | <!--[if gte mso 14]> | Version comparison | | !mso <version> | <!--[if !mso 16]> | Not this version | | IE / !IE | <!--[if IE]> | Legacy Internet Explorer conditions | | <op> IE <version> | <!--[if gte IE 8]> | IE version comparison | | Compound & / \| | <!--[if (gt mso 9)&(lte mso 11)]> | AND / OR |

Valid operators: gte, gt, lte, lt, eq

Valid Outlook versions: 9 (2000), 10 (2002), 11 (2003), 12 (2007), 14 (2010), 15 (2013), 16 (2016/2019/365)

Note: there is no MSO version 13 — Outlook skips from 12 (2007) to 14 (2010).

License

MIT