Preventing tab to cycle through address bar

问题

I realize this is probably an accessibility issue that may best be left alone, but I'd like to figure out if it possible to prevent the tab from visiting the address bar in the tabbing cycle.

My application has another method of cycling through input areas, but many new users instinctively try to use the tab, and it doesn't work as expected.

回答1:

Here's a generic jquery implementation where you don't have to find the max tab index. Note that this code will also work if you add or remove elements in your DOM.

$('body').on('keydown', function (e) {
    var jqTarget = $(e.target);
    if (e.keyCode == 9) {

        var jqVisibleInputs = $(':input:visible');
        var jqFirst = jqVisibleInputs.first();
        var jqLast = jqVisibleInputs.last();

        if (!e.shiftKey && jqTarget.is(jqLast)) {
            e.preventDefault();
            jqFirst.focus();
        } else if (e.shiftKey && jqTarget.is(jqFirst)) {
            e.preventDefault();
            jqLast.focus();
        }
    }
});

However, you should note that the code above will work only with visible inputs. Some elements may become the document's activeElement even if they're not input so if it's your case, you should consider adding them to the $(':input:visible') selector.

I didn't add code to scroll to the focus element as this may not be the wanted behavior for everyone... if you need it, just add it after the call to focus()

回答2:

You could use Javascript and capture the "keydown" event on the element with the highest "tabindex". If the user presses the "TAB" key (event.keyCode==9) without the "Shift" key (event.shiftKey == false) then simply set the focus on the element with the lowest tabindex.

You would then also need to do the same thing in reverse for the element with the lowest tabindex. Capture the "keydown" event for this element. If the user presses the "TAB" key (event.keyCode==9) WITH the "Shift" key (event.shiftKey == true) then set the focus on the element with the highest tabindex.

This would effectively prevent the address bar from ever being focused using the TAB key. I am using this technique in my current project.

Dont forget to cancel the keydown event if the proper key-combination is pressed! With JQuery it's "event.preventDefault()". In standard Javascript, I believe you simply "return false".

Here's a JQuery-laden snippet I'm using...

    $('#dos-area [tabindex=' + maxTabIndex + ']').on('keydown', function (e) {
        if (e.keyCode == 9 && e.shiftKey == false) {
            e.preventDefault();
            $('#dos-area [tabindex=1]').focus();
        }
    });
    $('#dos-area [tabindex=1]').on('keydown', function (e) {
        if (e.keyCode == 9 && e.shiftKey == true) {
            e.preventDefault();
            $('#dos-area [tabindex=' + maxTabIndex + ']').focus();
        }
    });

Also keep in mind that setting tabindex=0 has undesirable results on the order in which things are focused. I always remember (for my purposes) that tabindex is a 1-based index.

回答3:

You can control the tabbing order (and which elements should be able to get focus at all) with the global tabindex attribute.

However, you can't prevent users to tab into another context not under control of the page (e.g. the browser's address bar) with this attribute. (It might be possible in combination with JavaScript, though.)

For such a (evil!) use case, you'd have to look into keyboard traps.

WCAG 2.0 has the guideline: 2.1.2 No Keyboard Trap. In Understanding SC 2.1.2 you can find "Techniques and Failures" for this guideline:

F10: Failure of Success Criterion 2.1.2 and Conformance Requirement 5 due to combining multiple content formats in a way that traps users inside one format type
FLASH17: Providing keyboard access to a Flash object and avoiding a keyboard trap
G21: Ensuring that users are not trapped in content

So maybe you get some ideas by that how such a trap would be possible.

回答4:

I used to add two tiny, invisible elements on tabindex 1 and on the last tabindex. Add a onFocus for these two: The element with tabindex 1 should focus the last real element, the one with the max tabindex should focus the first real element. Make sure that you focus the first real element on Dom:loaded.

回答5:

I used m-albert solution and it works. But in my case I do not control the tabindex properties. My intention is set the focus on a toolbar at the top of the page (first control) when user leaves the last control on the page.

$(':input:visible').last().on('keydown', function (e) {
    if (e.keyCode == 9 && e.shiftKey == false) {
        e.preventDefault();
        $('html, body').animate({
            scrollTop: 0
        }, 500);
        $(':input:visible', context).first().focus();
    }
});

Where context can be any Jquery object, selector, or even document, or you can omit it.

The scrolling animation, of course, is optional.

回答6:

Not sure if this is still a issue, but I implemented my own solution that does not use jQuery, can be used in the case when all the elements have tabindex="0", and when the DOM is subject to change. I added an extra argument for a context if you want to limit the tabcycling to a specific element containing the tabindex elements.

Some brief notes on the arguments:

min must be less than or equal to max, and contextSelector is an optional string that if used should be a valid selector. If contextSelector is an invalid selector or a selector that doesn't match with any elements, then the document object is used as the context.

function PreventAddressBarTabCyle(min, max, contextSelector) {
    if( isNaN(min) ) throw new Error('Invalid argument: first argument needs to be a number type.')
    if( isNaN(max) ) throw new Error('Invalid argument: second argument needs to be a number type.')
    if( max < min ) throw new Error('Invalid arguments: first argument needs to be less than or equal to the second argument.')
    min = min |0;
    max = max |0;
    var isDocumentContext = typeof(contextSelector) != 'string' || contextSelector == '';

    if( min == max ) {
        var tabCycleListener = function(e) {
            if( e.keyCode != 9 ) return;

            var context = isDocumentContext ? document : document.querySelector(contextSelector);
            if( !context && !('querySelectorAll' in context) ) {
                context = document;
            }

            var tabindexElements = context.querySelectorAll('[tabindex]');
            if( tabindexElements.length <= 0 ) return;
            var targetIndex = -1;
            for(var i = 0; i < tabindexElements.length; i++) {
                if( e.target == tabindexElements[i] ) {
                    targetIndex = i;
                    break;
                }
            }
            // Check if tabbing backward and reached first element
            if( e.shiftKey == true && targetIndex == 0 ) {
                e.preventDefault();
                tabindexElements[tabindexElements.length-1].focus();
            }
            // Check if tabbing forward and reached last element
            if( e.shiftKey == false && targetIndex == tabindexElements.length-1 ) {
                e.preventDefault();
                tabindexElements[0].focus();
            }
        };
    } else {
        var tabCycleListener =  function(e) {
            if( e.keyCode != 9 ) return;

            var context = isDocumentContext ? document : document.querySelector(contextSelector);
            if( !context && !('querySelectorAll' in context) ) {
                context = document;
            }

            var tabindex = parseInt(e.target.getAttribute('tabindex'));
            if( isNaN(tabindex) ) return;
            // Check if tabbing backward and reached first element
            if (e.shiftKey == true && tabindex == min) {
                e.preventDefault();
                context.querySelector('[tabindex="' + max + '"]').focus();
            } 
            // Check if tabbing forward and reached last element
            else if (e.shiftKey == false && tabindex == max) {
                e.preventDefault();
                context.querySelector('[tabindex="' + min + '"]').focus();
            }
        };
    }
    document.body.addEventListener('keydown', tabCycleListener, true);
}

More notes:

If min is equal to max, then tab cycling will occur naturally until the last element in the context is reached. If min is strictly less than max, then tabbing will cycle naturally until either the min or the max is reached. If tabbing backwards and the min is reached, or tabbing forward and the max is reached, then the tabbing will cycle to the min element or max element respectively.

Example usage:

// For all tabindex elements inside the document
PreventAddressBarTabCyle(0,0);
// Same as above
PreventAddressBarTabCyle(1,1);
// NOTE: if min == max, the tabindex value doesn't matter
//    it matches all elements with the tabindex attribute

// For all tabindex elements between 1 and 15
PreventAddressBarTabCyle(1,15);
// For tabindex elements between 1 and 15 inside
//   the first element that matches the selector: .some-form
PreventAddressBarTabCyle(1,15, '.some-form');
// For all tabindex elements inside the element
//   that matches the selector: .some-form2
PreventAddressBarTabCyle(1,1, '.some-form2');

来源：https://stackoverflow.com/questions/15355948/preventing-tab-to-cycle-through-address-bar

标签

browser

user-interface

accessibility