REParse.js

Compose a structured data from unstructured text using regex-based pattern matching. This was originally used in UAParser.js, it basically just loops through a list of regexes, if a match was found then the matched data will be assigned to the result.

npm i re-parse-js

Methods

use(re: [RegExp[], REMapper[]][]): REParse

parse(str: string): REsult

Code Examples

General Schema

[
    [
        RegExp[], 
        REMapper[]
    ],
    [
        RegExp[], 
        REMapper[]
    ],
    ...
]

where

RegExp[] => [ a list of RegExp instances that capture the values ]
REMapper[] => [ a list of rules on how to map the captured values into result properties ]
    - string                                # prop = $match 
    - [string, string]                      # prop = string
    - [string, Function]                    # prop = func($match)
    - [string, Function, any]               # prop = func($match, arg)
    - [string, RegExp, string]              # prop = $match.replace(regex, string)
    - [string, RegExp, string, Function]    # prop = func($match.replace(regex, string))

1. Directly assign the captured match into result properties

• Example 1.1: parsing user-agent

const remap = [
    [
        [
            /(mozilla)\/([\d\.]+)/i, 
            /(msie)\/([\d\.]+)/i
        ],
        ['browser', 'version']
    ],
    [
        [
            /(opera)\/((\d)\.[\d\.]+)/i
        ], 
        ['browser', 'version', 'major']
    ]
];
const str1 = 'Mozilla/5.0';
const str2 = 'Opera/1.2';

const re = new REParse();
re.use(remap);
re.parse(str1);
// { browser: 'Mozilla', version: '5.0' }
re.parse(str2);
// { browser: 'Opera', version: '1.2', major: '1' }

• Example 1.2: parsing URL

const remap = [
    [
        [
            /(https?):\/\/(\w+\.\w+)\/(.*)\?(.+)/
        ],
        ['protocol', 'host', 'path', 'query']
    ]
];
const urlString = 'https://faisalman.com/?ref=github';

const re = new REParse(remap);
re.parse(urlString);
// { protocol: 'https', host: 'faisalman.com', path: '', query: 'ref=github' }

2. Post-process the captured match before assigning to result

A. Direct value replacement

const remap = [
    [
        [
            /(facebook)\/(\d+)/, 
            /(whatsapp)\/(\d+)/, 
            /(instagram)\/(\d+)/
        ],
        [['browser', 'Meta'], 'version'] // Always assign 'Meta' regardless matched value
    ]
];
const str = 'facebook/100';

new REParse().use(remap).parse(str);
// { browser: 'Meta', version: '100' }

B. Replace-based value replacement

const remap = [
    [
        [
            /(comodo_dragon)\/(\d+)/i
        ],
        [['browser', /(\w+)_(\w{3})\w+/ig, '$1 $2cula'], 'version'] // Replace captured data, see string.replace
    ]
];
const str = 'Comodo_Dragon/99';

new REParse().use(remap).parse(str);
// { browser: 'Comodo Dracula', version: '99' }

C. Function-based value replacement

const lowerize = str => str.toLowerCase();
const remap = [
    [
        [
            /(ARM)(64)/
        ],
        [['arch', lowerize], 'bitness'] // Pass the captured match into function()
    ],
    [
        [
            /(x86)-(64)/
        ],
        ['arch', 'bitness'] // Direct assignment
    ]
];
const str1 = 'ARM';
const str2 = 'x86-64';

const re = new REParse()
re.use(remap)
re.parse(str1); // { arch: 'arm', bitness: '64' }
re.parse(str2); // { arch: 'x86', bitness: '64' }

License

MIT License

Copyright (c) 2023-2025 Faisal Salman <f@faisalman.com>

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.