Method on

shepherd.js/src/evented.ts:22–32

* Adds an event listener for the given event string. * * @param {string} event * @param {Function} handler * @param ctx * @param {boolean} once * @returns

(event: string, handler: AnyHandler, ctx?: unknown, once = false)

   * @returns
   */
  on(event: string, handler: AnyHandler, ctx?: unknown, once = false) {
    if (isUndefined(this.bindings)) {
      this.bindings = {};
    }
    if (isUndefined(this.bindings[event])) {
      this.bindings[event] = [];
    }
    this.bindings[event]?.push({ handler, ctx, once });

    return this;
  }

  /**
   * Adds an event listener that only fires once for the given event string.