Dynamically Adjust HTML Text Input Width to Content

Use onkeypress even

see this example :http://jsfiddle.net/kevalbhatt18/yug04jau/7/

<input id="txt" placeholder="name" class="form" type="text" onkeypress="this.style.width = ((this.value.length + 1) * 8) + 'px';"></span>

And for placeholder on load use jquery and apply placeholder size in to input

$('input').css('width',((input.getAttribute('placeholder').length + 1) * 8) + 'px');

Even you can use id instead of input this is just an example so that I used $(input)

And in css provide min-width

.form {
    border: 1px solid black;
    text-align: center;
    outline: none;
    min-width:4px;
}

EDIT:

If you remove all text from input box then it will take placeholder value using focusout

Example: http://jsfiddle.net/kevalbhatt18/yug04jau/8/

$("input").focusout(function(){

    if(this.value.length>0){
        this.style.width = ((this.value.length + 1) * 8) + 'px';
    }else{
      this.style.width = ((this.getAttribute('placeholder').length + 1) * 8) + 'px';
    }

});

One possible way:

[contenteditable=true]:empty:before {
  content: attr(placeholder);
  color:gray;
}
/* found this online --- it prevents the user from being able to make a (visible) newline */
[contenteditable=true] br{
  display:none;
}

<p>Hello, my name is <span id="name" contenteditable="true" placeholder="name"></span>. I am <span id="age" contenteditable="true" placeholder="age"></span> years old.</p>

Source for CSS: http://codepen.io/flesler/pen/AEIFc.

You'll have to do some trickery to pick up the values if you need the values for a form.