AutoNumeric.js provides great formatting for currency/money input fields. I’ve used it in a few companies over the years.

Autonumeric demo

Here’s how to implement it in your Rails application with Stimulus:

bin/importmap pin autonumeric
rails g stimulus autonumeric

The importmap pin might fail, so a valid import from an url would be

# config/importmap.rb
-pin "autonumeric"
+pin "autonumeric", to: "https://ga.jspm.io/npm:autonumeric@4.6.0/dist/autoNumeric.min.js"

The Stimulus controller:

import { Controller } from "@hotwired/stimulus";
import AutoNumeric from "autonumeric";

export default class extends Controller {
  static values = {
    min: { type: Number, default: 0 },
    max: { type: Number, default: 999999.99 },
    currency: { type: String, default: "€" },
  };

  connect() {
    const autoNumericOptions = {
      decimalCharacter: ".",
      decimalPlaces: 2,
      digitGroupSeparator: ",",
      minimumValue: this.minValue,
      maximumValue: this.maxValue,
      unformatOnSubmit: true,
      currencySymbol: this.currencyValue,
      currencySymbolPlacement: "p", // 'p' for prefix
      modifyValueOnWheel: false,
    };

    new AutoNumeric(this.element, autoNumericOptions);
  }
}

Use in a rails text_field. Autonumeric requires you to use text_field, not number_field.

<%= form.text_field :name,
                    data: { controller: "autonumeric",
                            autonumeric_currency_value: "€",
                            autonumeric_min_value: 0, autonumeric_max_value: 999999.99 },
                    class: "" %>

This will:

  • Automatically formats numbers as currency (e.g., “$1,234.56”)
  • Prevents invalid input
  • Handles decimal places correctly
  • Supports maximum value limits

P.S. Please always store money in bigint. Not integer or float. Stripe stores amounts in cents and so should you!