title: Getting comma in the joined array with string
body: <p>I don't know why I have a comma when I use <code>join</code> method. Can anyone explain?</p>
  
  <p><div class="snippet" data-lang="js" data-hide="false" data-console="true" data-babel="false">
  <div class="snippet-code">
  <pre class="snippet-code-js lang-js prettyprint-override"><code>function maskify(cc) {
    var a = cc.slice(cc.length - 4, cc.length);
    var b = cc.slice(0, cc.length - 4);
    b = b.split("");
    for (var i = 0; i &lt; b.length; i++) {
      b[i] = "#";
  
    }
    b.join("#");
    console.log(b + a);
  }
  
  maskify("sadasdasdasdasdasd");
  // result : #,#,#,#,#,dasd</code></pre>
  </div>
  </div>
  </p>