Creating a Textbox with JavaScript Auto-Complete | WebReference

Creating a Textbox with JavaScript Auto-Complete

Creating a Textbox with JavaScript Auto-Complete

Many readers are probably familiar with the Auto-Complete feature of Internet Explorer (see Fig.1 below). For each text box with a specified name, the browser maintains a list of values that the user has entered. As the user types in a new value, it pops up the list to save the user from having to type it all in.

Fig. 1: Auto-Complete functionality in Internet Explorer.

This feature is useful in many contexts but there are some limitations:

    There is no control over what appears in this list. This can be annoying to the user if a value is entered incorrectly.

    Each list is associated with a text-box name, not a web site or page. As a consequence, the list is shared with other text boxes of the same name out on the web.

    It is not available in other browsers.

In this article I’ve presented a JavaScript answer to these problems. It allows the web site designer to determine in advance which Auto-Complete words to offer the user; it is specific to a single text-box and is cross-browser compatible (see Fig. 2).

Fig. 2: The JavaScript Auto-Complete solution.

The Auto-Complete functionality is handled in a class called AutoComplete…

  function AutoComplete(aStr, oText, oDiv, nMaxSize)
      // initialize member variables
      this.oText = oText; // the text box
      this.oDiv = oDiv; // a hidden <div> for the popup auto-complete
      this.nMaxSize = nMaxSize;

      // preprocess the texts for fast access
      this.db = new AutoCompleteDB();
      var i, n = aStr.length;
      for ( i = 0; i < n; i++ )

      // attach handlers to the text-box
     oText.AutoComplete = this;
      oText.onkeyup = AutoComplete.prototype.onTextChange;
      oText.onblur = AutoComplete.prototype.onTextBlur;

The first argument to the AutoComplete constructor is an array of strings that defines the AutoComplete list. This list is fed into a tree structure managed by another class called AutoCompleteDB (more on this later). The other arguments are: the text-box object, a DIV object for displaying the Auto-Complete popup and the maximum amount of Auto-Complete options to offer at any one time.

The AutoComplete code needs to attach a couple of handlers to the text-box; an onkeyup handler reacts each time the user types a character into the text-box and gives the opportunity to offer suggestions. The onblur handler gives the chance to hide any popup that might be visible when the focus leaves the text-box. The implementation of these handlers is shown here…

AutoComplete.prototype.onTextBlur = function()

AutoComplete.prototype.onblur = function()
  { = "hidden";

AutoComplete.prototype.onTextChange = function()

AutoComplete.prototype.onchange = function()
  var txt = this.oText.value;

  // count the number of strings that match the text-box value.
  var nCount = this.db.getCount(txt);

  // if a suitable number then show the popup-div
  if ( (this.nMaxSize == -1 ) || ((nCount < this.nMaxSize) && (nCount > 0)) )
      // clear the popup div.
      while ( this.oDiv.hasChildNodes() )

      // get all the matching strings from the AutoCompleteDB
      var aStr = new Array();
      this.db.getStrings(txt, "", aStr);

      // add each string to the popup-div
      var i, n = aStr.length;
      for ( i = 0; i < n; i++ )
          var oDiv = document.createElement('div');
          oDiv.innerHTML = aStr[i];
          oDiv.onmousedown = AutoComplete.prototype.onDivMouseDown;
          oDiv.onmouseover = AutoComplete.prototype.onDivMouseOver;
          oDiv.onmouseout = AutoComplete.prototype.onDivMouseOut;
          oDiv.AutoComplete = this;
 = "visible";
      else // hide the popup-div
          this.oDiv.innerHTML = "";
 = "hidden";

Created: March 27, 2003
Revised: April 6, 2004