if (!user || typeof user.nam !== 'string') {
    throw new Error("Missing or invalid 'nam' on user");
  }

Contemporary JavaScript has optional chaining, default values, and reflective tools like Object.hasOwn, which are all web standards. You just have to know how to use them.

You really don't understand what types give you, do you?

Where are you going to put the code above in this:

  <section @name="user-details" class="user">

  <media :image="/app/icon/cc/{cc}.svg" :title="name">
    <p>{ email }</p>
  </media>

  <dl :if="org">
    <dt>Company</dt>      <dd>{ org }</dd>
    <dt>Country</dt>      <dd> { country }</dd>
    <dt>Company size</dt> <dd>{ size.desc } ({ size.label })</dd>
    <dt>Website</dt>      <dd><a class="action">{ website }</a></dd>
    <dt>Plan</dt>         <dd><pill icon="dot" :label="{ plan }"/></dd>
  </dl>

  <media-thumbs :items="shots"/>

  <chat-thread :thread="thread"/>

</section>

Are you going to write ifs for every permutation of possible typos? (Let's ignore for a second that it's not just typos)