The following code is flagged as dead (since it's *replacing* rather than updating the existing Object):
https://github.com/mozilla/pdf.js/blob/4483cba72410027acf46630ebf252ae529704476/src/core/xfa/template.js#L2336-L2339
according to the alert in https://github.com/mozilla/pdf.js/security/code-scanning/103?query=ref%3Arefs%2Fheads%2Fmaster

Looking at the surrounding code, I can see a couple of possibilities here:
 1. This is indeed just dead code, which should be removed.
 2. The code should be moved up, and placed just *above* the previous block instead.
 3. There should be other, more invasive, changes made to this code...

/cc @calixteman Which solution is correct here?
Assuming it's either option 1 or 2, I can submit a patch to fix this.
attributes,
      children,
    };
    const assist = this.assist ? this.assist[$toHTML]() : null;
    if (assist) {
      html.attributes.title = assist;
    }
    const borderStyle = this.border ? this.border[$toStyle]() : null;
    const bbox = computeBbox(this, html, availableSpace);
    const ui = this.ui[$toHTML]().html;
    if (!ui) {
      Object.assign(style, borderStyle);
      return HTMLResult.success(createWrapper(this, html), bbox);
    }
    if (this[$tabIndex]) {
      if (ui.children && ui.children[0]) {
        ui.children[0].attributes.tabindex = this[$tabIndex];
      } else {
        ui.attributes.tabindex = this[$tabIndex];
      }
    }
    if (!ui.attributes.style) {
      ui.attributes.style = Object.create(null);
    }
    if (this.ui.button) {
      Object.assign(ui.attributes.style, borderStyle);
    } else {
      Object.assign(style, borderStyle);
    }
    children.push(ui);