mine/node_modules/webpack-dev-server/client/overlay/state-machine.js

import createMachine from "./fsm.js";

/**
 * @typedef {Object} ShowOverlayData
 * @property {'warning' | 'error'} level
 * @property {Array<string  | { moduleIdentifier?: string, moduleName?: string, loc?: string, message?: string }>} messages
 * @property {'build' | 'runtime'} messageSource
 */

/**
 * @typedef {Object} CreateOverlayMachineOptions
 * @property {(data: ShowOverlayData) => void} showOverlay
 * @property {() => void} hideOverlay
 */

/**
 * @param {CreateOverlayMachineOptions} options
 */
var createOverlayMachine = function createOverlayMachine(options) {
  var hideOverlay = options.hideOverlay,
    showOverlay = options.showOverlay;
  var overlayMachine = createMachine({
    initial: "hidden",
    context: {
      level: "error",
      messages: [],
      messageSource: "build"
    },
    states: {
      hidden: {
        on: {
          BUILD_ERROR: {
            target: "displayBuildError",
            actions: ["setMessages", "showOverlay"]
          },
          RUNTIME_ERROR: {
            target: "displayRuntimeError",
            actions: ["setMessages", "showOverlay"]
          }
        }
      },
      displayBuildError: {
        on: {
          DISMISS: {
            target: "hidden",
            actions: ["dismissMessages", "hideOverlay"]
          },
          BUILD_ERROR: {
            target: "displayBuildError",
            actions: ["appendMessages", "showOverlay"]
          }
        }
      },
      displayRuntimeError: {
        on: {
          DISMISS: {
            target: "hidden",
            actions: ["dismissMessages", "hideOverlay"]
          },
          RUNTIME_ERROR: {
            target: "displayRuntimeError",
            actions: ["appendMessages", "showOverlay"]
          },
          BUILD_ERROR: {
            target: "displayBuildError",
            actions: ["setMessages", "showOverlay"]
          }
        }
      }
    }
  }, {
    actions: {
      dismissMessages: function dismissMessages() {
        return {
          messages: [],
          level: "error",
          messageSource: "build"
        };
      },
      appendMessages: function appendMessages(context, event) {
        return {
          messages: context.messages.concat(event.messages),
          level: event.level || context.level,
          messageSource: event.type === "RUNTIME_ERROR" ? "runtime" : "build"
        };
      },
      setMessages: function setMessages(context, event) {
        return {
          messages: event.messages,
          level: event.level || context.level,
          messageSource: event.type === "RUNTIME_ERROR" ? "runtime" : "build"
        };
      },
      hideOverlay: hideOverlay,
      showOverlay: showOverlay
    }
  });
  return overlayMachine;
};
export default createOverlayMachine;