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react-rxinput React extends input element to validate against a regular expression as you type input (incremental regex matcher)


Version published
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  • Removed bootstrap dependency and made the component UI neural and the expense of reduced visual functionality.
  • The functionality can be reintroduced through customization


  • React Component
  • Input component
  • RegExp to define - validation, masks, ...
  • Not require coding to for most validation


I stared with a simple challange, how can I make input validation both easy to usefor developes and anso easy to use for the end user.So lets start with very simple usecase usecase:

  • Enter a phone number: 3 digit area-code, 3 digit exchange and 4 digit number
  • Options
    1. No validation - Just use an input box and allow user to enter anything
    2. Application validation - allow user to enter anything, the application checks the format when the form is submitted
    3. Form validation in Javascript - allow user to enter anything, trap the onsubmit event and use a regular expression to validate the text in the input field; perhaps a regular expression like this /\d{3} \d{3} \d{4}/, just as a reminder \d will match any digit, and \d{3} will match 3 digits.

See Wiki for more technical details

A flexible input validation widget that validates you input as you type. You use a regular expression to validate the input. As all tools this little component scratches an itch - needed an form input component that would allow only valid input, guide the user as he or she in typing in the input text, perform full/partial auto complete. Most of all it should use validation components that is standard, and there is nothing more standard that regular expressions for string matching. The only problem is that JavaScript RegExp requires the entire input before it can validate. Use incr-regex-package implements a stream (one character at a time RegExp matching). Note: not intenders to replace JavaScript RegExp, an alternative to regexp for these use cases.

This component was inspired by react-maskinput a component to support fixed masked input, e.g. phone number, credit card, etc. The good thing is that it does validation as you type, but the validation is very limited (you can create your custom validation code - but you have to code). The description of the mask is easy but not very flexible and is specific to this component.



  • Good support for fixed format entry (mask input) - example Phone number, date, credit card number
  • Semi-fixed format, for example URL, email
  • Mix of from a fixed list (dropdown list) and user entry formats
  • Easy to use (my opinion)
  • Use regular expression to define 'masked input' react-maskinput
  • RegExp matching/validation as you type
  • Auto complete
  • Matching suggestions
  • An alternative for react-maskinput
  • Handles very large regular expressions
  • Pretty extensive test scripts


Demo notes:

  • Has some pre-canned regular expressions
  • You can try your own regular expression
  • Note: Does not error check your regular expression (bare with me I will fix that)

Please try out the demo


rxinput demo


JavaScript regular expression is great and really fast, and it would be pointless to try to create a RegExp alternative that does the same thing. But having said that, this project is a specific use case - validating input as you type using RegExp.

I needed a regular expression matcher that would work incrementally; by that I mean that it should let you know if a string matches the beginning part of a regular expression (good so far, but needs more input scenario). I tried to figure out if that was possible using JavaScript's regular expression matcher. I could not figure out any easy to do that. I decided that I would write an incremental regular expression matcher. I was much more difficult that I expected. But I have build an npm package that does perform incremental regular expression matching.

The widget was inspired by another github project (https://github.com/insin/react-maskedinput) that provides mask input for things like phone number, credit card number, date and so on. Although the capability is very nice, but it was limited. THe input mask you could enter has very little flexibility, wile a regular expression has all the flexibility you could need (even regexp has its limitations, cannot match recursive patterns, but that is for another day).

While building the widget it became obvious that it could be a swiss army knife and provide the following (so I implemented them):

  • Auto completion
  • Dropdown list alternative
  • Radio button alternative
  • Mask input replacement
  • As you type validation
  • Force upper case
  • Limit the character you can enter based on matching the regular expression
  • Only allow valid input as you type


  • Currently only works as React component, requiring bootstrap 3 and also react-bootstrap

  • Working on lifting the limitation and offering jQuery plugin (i have never built a jquery plugin, so it might take a little time). * Further I would like to offer a version that does not depend on any external js library.

  • RegExp (incr-regex-package)

  • Does not support look back

  • Does not support look forward

  • Is not a replacement JavaScript RegExp

  • Tries to have test cases for quite a lot of regexp variotions, but cannot be sure of all RegExp edge cases are handles, use the demo app to try out your regexp.

  • Assumes all reagep are anchored to the beging of input (meaning the regexp matching always starts at the begining

Known bugs

  • Rare: but deleting input text in the middle of the input box (very complex regular expressions) sometimes misbehaves.
  • The algorithm for handling this is rather complex. I am trying to figure out how to imp-lement the capability more elegantly.


npm install react-rxinput --save


git clone https://github.com/nurulc/react-rxinput.git cd react-rxinput npm install npm start

The commands above will start the demo application point youy browser at http://localhost:3000

How to use the component:

Use it where you might have used <input element, take all the properties of a regular input element

RxInput specific properties:

  • mask - regular expression
  • value - value to set
  • selection - selection
  • popover - Yes| No whether to show hints or nor
  • onChange - function to execute when a chnage happens
const App = React.createClass({ getInitialState() { return { color: "", } }, _onChange(e) { this.setState({color: e.target.value}) }, render() { // Some regular expression you could try // const email = /[a-zA-Z0-9._-]+@[a-zA-Z0-9._-]+/; // const phone = /(\\+\\d{1,3} )?\\(\\d{3}\\)-\\d{3}-\\d{4}( Ext: \\d+)?/; // const color = /Red|Gr(een|ay)|Blue|Yellow|O(range|live)/; // A rather complex regular expression (please feel free to user your own) const color = /Color: (Red|Gr(een|ay)|Blue|Yellow|O(range|live))|Email: [a-zA-Z0-9._-]+@[a-zA-Z0-9._-]+|(Phone: (\\+\\d{1,3} )?\\(\\d{3}\\)-\\d{3}-\\d{4}( Ext: \\d+)?)/; return ( <div className="App"> <div> <div className="form-field"> <label htmlFor="color">Color:</label> <RxInput name="color" id="color" size="40" mask={color} value={this.state.color} popover="yes" placeholder="Color: <scome colors> | Email: <email> | Phone: <phone number>" onChange={this._onChange}/> </div> </div> </div> ) } }); render(<App name="test"/>, document.querySelector('#demo'));

Documentation to come



Last updated on 28 Jan 2020

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