Adjust width of input field to its input

To calculate the width of the current input, you'll have to embed it in a temporary span element, attach that thing to the DOM, get the computed width (in pixels) using the scrollWidth property and remove the span again. Of course you'll have to ensure that the same font family, font size, etc., is used in the input as well as in the span element. Therefore I assigned the same class to them.

I attached the function to the keyup event, as on keypress the input character is not yet added to the input value, so that will result in the wrong width. Unfortunately, I don't know how to get rid of the scrolling of the input field (when adding characters to the end of the field); it scrolls, because the character is added and shown before adjustWidthOfInput() is called. And, as said, I can't do this the other way round because then you'll have the value of the input field before the pressed character is inserted. I'll try to solve this issue later.

BTW, I only tested this in Firefox (3.6.8), but you'll get the point, I hope.

<!DOCTYPE html>
<html>
  <head>
    <meta charset="utf-8">
    <title>Get/set width of &lt;input&gt;</title>
    <style>
      body {
        background: #666;
      }

      .input-element {
        border: 0;
        padding: 2px;
        background: #fff;
        font: 12pt sans-serif;
      }

      .tmp-element {
        visibility: hidden;
        white-space: pre;
      }
    </style>
  </head>
  <body>
    <input id="theInput" type="text" class="input-element" value="1">
    <script>
      var inputEl = document.getElementById("theInput");

      function getWidthOfInput() {
        var tmp = document.createElement("span");
        tmp.className = "input-element tmp-element";
        tmp.innerHTML = inputEl.value.replace(/&/g,'&amp;').replace(/</g,'&lt;').replace(/>/g,'&gt;');
        document.body.appendChild(tmp);
        var theWidth = tmp.getBoundingClientRect().width;
        document.body.removeChild(tmp);
        return theWidth;
      }

      function adjustWidthOfInput() {
        inputEl.style.width = getWidthOfInput() + "px";
      }

      adjustWidthOfInput();
      inputEl.onkeyup = adjustWidthOfInput;
    </script>
  </body>
</html>

It sounds like your expectation is that the style be applied dynamically to the width of the textbox based on the contents of the textbox. If so you will need some js to run on textbox contents changing, something like this:

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

Note: this solution only works when every character is exactly 8px wide. You could use the CSS-Unit "ch" (characters) which represents the width of the character "0" in the chosen font. You can read about it here.


In modern browser versions, CSS unit ch is also available. To my understanding, it is font-independent unit, where 1ch equals to width of character 0 (zero) in any given font.

Thus, something as simple as following could be used as resize function, by binding to the input event:

var input = document.querySelector('input'); // get the input element
input.addEventListener('input', resizeInput); // bind the "resizeInput" callback on "input" event
resizeInput.call(input); // immediately call the function

function resizeInput() {
  this.style.width = this.value.length + "ch";
}
input{ font-size:1.3em; padding:.5em; }
<label>Text
  <input>
</label>

That example would resize the input to length of the value + 2 characters extra.

One potential problem with the unit ch is that in many fonts (i.e. Helvetica) the width of the character "m" exceeds the width of the character 0 and the character "i" is much narrower. 1ch is usually wider than the average character width, usually by around 20-30% according to this post.

Tags:

Javascript

Html

Css

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