Maybe/app/javascript/controllers/deletion_controller.js

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

export default class extends Controller {
  static targets = ["replacementField", "submitButton"];
  static classes = ["dangerousAction", "safeAction"];
  static values = {
    submitTextWhenReplacing: String,
    submitTextWhenNotReplacing: String,
  };

  updateSubmitButton() {
    if (this.replacementFieldTarget.value) {
      this.submitButtonTarget.value = this.submitTextWhenReplacingValue;
      this.#markSafe();
    } else {
      this.submitButtonTarget.value = this.submitTextWhenNotReplacingValue;
      this.#markDangerous();
    }
  }

  #markSafe() {
    this.submitButtonTarget.classList.remove(...this.dangerousActionClasses);
    this.submitButtonTarget.classList.add(...this.safeActionClasses);
  }

  #markDangerous() {
    this.submitButtonTarget.classList.remove(...this.safeActionClasses);
    this.submitButtonTarget.classList.add(...this.dangerousActionClasses);
  }
}