[CSS] Transform a button to a text input

Here is a cool CSS trick I found for actions that require a text value:

Animated GIF of the control

See the code in action on CodePen

HTML

<form id='buttonWithText' onSubmit={this.onSubmit}>  
  <div id='slider' class='collapsed'>
    <input type='button' id='toggle' value='Change username'>
    <input type='text' id='input' tabindex='-1' placeholder='username' size=10>
    <input type='submit' id='ok' tabindex='-1' value='ok'>
  </div>
</form>  

CSS

#buttonWithText {
  overflow: hidden;
  width: 200px;
}

#slider {
  display: flex;
  width: 200%;
  transition: 0.5s;
}

#slider.expanded {
  transform: translateX(-50%);
}

#toggle {
  flex: 0 0 50%;
}

#input {
  flex: auto;
}

#ok {
  flex: none;
}

JavaScript

function expand() {  
  slider.className = 'expanded';
  setTimeout(function() {
    input.focus();
  }, 500);
}

function collapse() {  
  slider.className = 'collapsed';
  input.blur();
}

toggle.onclick = expand;

input.onblur = function() {  
  setTimeout(collapse, 100);
}

buttonWithText.onsubmit = function(e) {  
  e.preventDefault();
  alert("New username: " + input.value);
  collapse();
}