Dynamically expand height of input type “text” based on number of characters typed into field

Question

Similar to the below JSFiddle (which I bookmarked and do not know from where the original question emerged):

http://jsfiddle.net/mJMpw/6/

Answer 1

As others explained, input field can't have multiline text, you should use textarea to mimic an input field, and jQuery to make it auto resize vertically (with fixed width).

JS:

//This span is used to measure the size of the textarea
//it should have the same font and text with the textarea and should be hidden
var span = $('').css('display','inline-block')
                      .css('word-break','break-all')
                      .appendTo('body').css('visibility','hidden');
function initSpan(textarea){
  span.text(textarea.text())
      .width(textarea.width())
      .css('font',textarea.css('font'));
}
$('textarea').on({
    input: function(){
       var text = $(this).val();      
       span.text(text);      
       $(this).height(text ? span.height() : '1.1em');
    },
    focus: function(){           
       initSpan($(this));
    },
    keypress: function(e){
       //cancel the Enter keystroke, otherwise a new line will be created
       //This ensures the correct behavior when user types Enter 
       //into an input field
       if(e.which == 13) e.preventDefault();
    }
});

CSS:

textarea {
  width:200px;
  resize:none;
  overflow:hidden;
  font-size:18px;
  height:1.1em;
  padding:2px;
}

Demo.

Updated Demo:

This new updated demo has some bugs fixed and it also supports Enter key, max-height limit, the width does not need to be set fixedly at first (instead we can set its min-width). It's much more full-featured.

Updated Demo