SOURCE

var btn = document.getElementById('btn');
var isShow = true;
btn.onclick = function() {
  var box = document.getElementById('box');
  if (isShow) {
  box.className = 'hidden';
  this.value = 'show';
    isShow = false;
  } else {
    box.className = 'show';
    this.value = 'hide';
    isShow = true;
  }
}
                            

<input type="button" id="btn" value="hide"/>
<br>
<div id="box"></div>

#box {
  background-color:red;
  width: 200px;
  height: 200px;
}
.hidden {
  display: none;
}
.show {
  display: block;
}