title: My for-loop get a more character, it do not pass my judgement
body: <p>I use the bellow code to get my requirement text:</p>
  
  <pre><code>var ipv4s = [
    {ip: '1.1.1.1'},
    {ip: '1.1.1.2'},
    {ip: '1.1.1.3'},
    {ip: '1.1.1.4'},
    {ip: '1.1.1.5'},
    {ip: '1.1.1.6'},
  ]
  
  var ip_text = ''
  for (let index in ipv4s) {
  
    var item = ipv4s[index]
  
    if(index === (ipv4s.length -1) ){
  
      ip_text += item.ip
    }else {
      ip_text += (item.ip + ", ")
    }
    console.log(index, ipv4s.length - 1)
  }
  
  console.log(ip_text)
  </code></pre>
  
  <p>But I get the bellow console:</p>
  
  <pre><code>0 5
  1 5
  2 5
  3 5
  4 5
  5 5
  1.1.1.1, 1.1.1.2, 1.1.1.3, 1.1.1.4, 1.1.1.5, 1.1.1.6, 
  </code></pre>
  
  <p>But in my think it will get the <code>1.1.1.1, 1.1.1.2, 1.1.1.3, 1.1.1.4, 1.1.1.5, 1.1.1.6</code>. </p>
  
  <p>why there is a redundant <code>,</code> in there?</p>