title: merge two JavaScript objects with priority
body: <p>I have two JavaScript objects like</p>
  
  <pre><code>let master = {A:0, B:2};
  let slave = {B:1, C:1};
  </code></pre>
  
  <p>I need:</p>
  
  <pre><code>result == {A:0, B:2, C:1};
  </code></pre>
  
  <p>Does JS have a simple command to merge in that way?</p>