title: best way to join map keys/values comma separated
body: <p>I have a map that looks like (it's not constant and there could be more subarrays)</p>
  
  <pre><code>var mMp=    new Map([
      [ "A", [1, "r"] ],
      [ "B", [2, "d "]]
      ]);
  </code></pre>
  
  <p>I am trying to get to:</p>
  
  <pre><code>var ks = "A, B"
  var vs1 = "1, 2"
  var vs2 = "r, d"
  </code></pre>
  
  <p>I could do </p>
  
  <pre><code>mMp.forEach( (val, key) =&gt; {.....};
  </code></pre>
  
  <p>where I add the stuff manually, but I'd have to check for the last value. I also thought about </p>
  
  <pre><code>Array.from(mMp.keys()).join(", ");
  </code></pre>
  
  <p>but that also would not help with the values, i guess. And it's less efficient, although I'm not too worried about efficiency here.</p>
  
  <p>What's the best way I can get those 3 sets for strings?
  Thank you!</p>