Making ‘previous/next topic’ keyboard shortcuts into a theme component

Development
3

Thank you, @merefield! I am stuck (at least I think that’s where :nerd_face: ) at the javascript snippet for the back button…

discourse-tc-topic-next-button/javascripts/discourse/components/topic-previous-button.js at master · denvergeeks/discourse-tc-topic-next-button · GitHub where at the moment I have this…

import Component from '@glimmer/component';
import { action } from '@ember/object';
import { tracked } from '@glimmer/tracking';
import {
  nextTopicUrl,
  previousTopicUrl,
} from "discourse/lib/topic-list-tracker";
import DiscourseURL from "discourse/lib/url";
import { inject as service } from "@ember/service";

export default class TopicPreviousButton extends Component {
  @service site;
  @tracked label = "";
  @tracked showButton = false;
  @tracked lastURL = "";

  constructor(owner, args) {
    super(owner, args);
    previousTopicUrl().then((url) => {
      if (url) {
        this.showButton = true;
        this.lastURL = url;
      } else {
        this.showButton = false;
        this.lastURL = "";
      }
    })
  };

  get goFirst() {
    return settings.topic_next_always_go_to_first_post
  }

  @action
  goToPreviousTopic() {
    let url;
    if (this.lastURL) {
      url = this.goFirst
        ? this.lastURL.substring(0, this.lastURL.nextIndexOf("/"))
        : this.lastURL;
      DiscourseURL.routeTo(url);
    }
  };
}

I think the problem is near the bottom at

? this.lastURL.substring(0, this.lastURL.nextIndexOf("/"))

Any thoughts?

I tried

? this.lastURL.substring(0, this.lastURL.indexOf("/"))