How do I keep my cursor/caret from moving inside of an input text element?

I'm trying to build a form that works in a manner similar to the Google Search page, as well as Gmail and several other pages (including the this page - see the "Tags" input on the Ask Question page). As text is input, a list of options will appear, and the user can use up and down arrows to select the option they want.

The problem I am having is that the up arrow puts the cursor/caret in position 0 of the field, and down puts it at the end. Is there an easy way of keeping it from moving to the beginning/end, or do I need to find the caret position before my function is r开发者_运维问答un, and reposition it to that spot after?

This is the beginning of the function that runs when when text is entered in the input element (onkeyup).

var keycode = checkKeycode (event);   // returns the keycode of the key pressed.
if (keycode == 38) {         // up arrow
    var selection = $(".optionsSelected").attr("id");
    var selId = parseInt(selection.replace('briefOption', ''));
    if (selId != 0) {
        $(".optionsSelected").removeClass("optionsSelected");
        var newSelId = selId - 1;
        $("#briefOption"+newSelId).addClass("optionsSelected");
    }
}
else if (keycode == 40) {     // down arrow
    var selection = $(".optionsSelected").attr("id");
    var selId = parseInt(selection.replace('briefOption', ''));
    if (selId != numAvEmps && numAvEmps != 0) {
        $(".optionsSelected").removeClass("optionsSelected");
        var newSelId = selId + 1;
        $("#briefOption"+newSelId).addClass("optionsSelected");
    }
}
else if (keycode == 27) {    // Escape
    $("#docDropDown").css("display","none");
}
else if (keycode == 9 || keycode == 13) {     //tab or enter
    /* Fill form */
}

Let me know if any more code would be useful. Thanks for the help.

---

You'd want to store the caret before and then when you're done doing things, set it back.

Something like this:

HTML body:

<input type="text" id="mytextbox" style="border: 1px solid black" />

Javascript:

function getCaretPosition(ctrl)
{
    var caretPos = 0;    
    // IE
    if (document.selection)
    {
        ctrl.focus ();
        var sel = document.selection.createRange();
        sel.moveStart ('character', -ctrl.value.length);
        caretPos = sel.text.length;
    }
    // Firefox
    else if (ctrl.selectionStart || ctrl.selectionStart == '0')
    {
        caretPos = ctrl.selectionStart;
    }

    return caretPos;
}

function setCaretPosition(ctrl, pos)
{
    if(ctrl.setSelectionRange)
    {
        ctrl.focus();
        ctrl.setSelectionRange(pos,pos);
    }
    else if (ctrl.createTextRange)
    {
        var range = ctrl.createTextRange();
        range.collapse(true);
        range.moveEnd('character', pos);
        range.moveStart('character', pos);
        range.select();
    }
}



$(document).ready(function ()
{

    $("#mytextbox").keydown(function (e)
    {
        // Up
        if(e.which == 38)
        {
            var pos = getCaretPosition(this);

            // Do stuff here that changes the value/caret?

            setCaretPosition(this, pos);
        }
        // Down
        else if(e.which == 40)
        {
            var pos = getCaretPosition(this);

            // Do stuff here that changes the value/caret?

            setCaretPosition(this, pos);
        }

    });

});

---

Just prevent the default action of the event. You can do this by returning false if you're using an event handler property rather than addEventListener/attachEvent, which would be the easiest way:

var input = document.getElementById("your_input");
var suppressKeypress = false;

input.onkeydown = function(evt) {
    evt = evt || window.event;
    var keyCode = evt.keyCode;
    if (keyCode == 38) {
        // Do your stuff here
        suppressKeypress = true; // For Opera; see below
        return false;
    }
    // Other cases here
};

// This bit is for Opera, which only allows you to suppress the default
// action of a keypress in the keypress event (not keydown)
input.onkeypress = function() {
    if (suppressKeypress) {
        suppressKeypress = false;
        return false;
    }
};