fabric.js/src/mixins/stateful.mixin.js

/*
  Depends on `stateProperties`
*/
fabric.util.object.extend(fabric.Object.prototype, /** @lends fabric.Object.prototype */ {

  /**
   * Returns true if object state (one of its state properties) was changed
   * @return {Boolean} true if instance' state has changed since `{@link fabric.Object#saveState}` was called
   */
  hasStateChanged: function() {
    return this.stateProperties.some(function(prop) {
      return this.get(prop) !== this.originalState[prop];
    }, this);
  },

  /**
   * Saves state of an object
   * @param {Object} [options] Object with additional `stateProperties` array to include when saving state
   * @return {fabric.Object} thisArg
   */
  saveState: function(options) {
    this.stateProperties.forEach(function(prop) {
      this.originalState[prop] = this.get(prop);
    }, this);

    if (options && options.stateProperties) {
      options.stateProperties.forEach(function(prop) {
        this.originalState[prop] = this.get(prop);
      }, this);
    }

    return this;
  },

  /**
   * Setups state of an object
   * @return {fabric.Object} thisArg
   */
  setupState: function() {
    this.originalState = { };
    this.saveState();

    return this;
  }
});