discourse/app/assets/javascripts/wizard/addon/components/image-preview-favicon.js

import { observes } from "discourse-common/utils/decorators";
import WizardPreviewBaseComponent from "./wizard-preview-base";

export default WizardPreviewBaseComponent.extend({
  width: 371,
  height: 124,
  tab: null,
  image: null,

  @observes("field.value")
  imageChanged() {
    this.reload();
  },

  images() {
    return { tab: "/images/wizard/tab.png", image: this.get("field.value") };
  },

  paint(options) {
    const { ctx, width, height } = options;
    this.scaleImage(this.tab, 0, 0, width, height);
    this.scaleImage(this.image, 40, 25, 30, 30);

    ctx.font = `20px 'Arial'`;
    ctx.fillStyle = "#000";

    let title = this.wizard.getTitle();
    if (title.length > 20) {
      title = title.substring(0, 20) + "...";
    }

    ctx.fillText(title, 80, 48);
  },
});