Question

I have a basic quantity field and would like to allow the user to increase/decrease the number within this input box based on the keyboard up/down.

Following on from: EndangeredMassa answer on keyboard code https://stackoverflow.com/a/375426/560287 how would I add this into a keyup function?

var keynum = 0;

if(window.event) { keynum = e.keyCode; }  // IE (sucks)
else if(e.which) { keynum = e.which; }    // Netscape/Firefox/Opera

if(keynum == 38) { // up
    //Move selection up
}

if(keynum == 27) { // down
    //Move selection down
}

Answer 1

//cache our input since we will be working with it each time an arrow key is pressed
var $input = $('input');

//bind the the `keydown` event for the `document` object which will catch all `keydown` events that bubble up the DOM
$(document).on('keydown', function (event) {

    //up-arrow (regular and num-pad)
    if (event.which == 38 || event.which == 104) {

        //make sure to use `parseInt()` so you can numerically add to the value rather than concocting a longer string
        $input.val((parseInt($input.val()) + 1));

    //down-arrow (regular and num-pad)
    } else if (event.which == 40 || event.which == 98) {
        $input.val((parseInt($input.val()) - 1));
    }
});

Here is a demo: http://jsfiddle.net/QRNP8/1/

Note that jQuery normalizes the charCode/keyCode properties into event.which:

Query normalizes the following properties for cross-browser
consistency:

target
relatedTarget
pageX
pageY
which
metaKey

Source: http://api.jquery.com/category/events/event-object/