jQuery 1.9 doesn't like leading whitespace from wp_ajax_add_menu_item

[csixty4]

jquery-migrate logs this message to the console when adding a new menu item:

JQMIGRATE: $(html) HTML strings must start with '<' character

Walker_Nav_Menu_Edit returns a <li> indented with two tabs because there's inline HTML in that class and it's indented. jQuery 1.9 rejects HTML strings with leading whitespace ​for security reasons.

(Note: this is probably why jquery-migrate is calling parseHTML instead of using a regex in #23055)

This patch uses $.parseHTML on the HTML fragment instead of passing it directly to $(). As it's written, $.parseHTML will strip out any scripts in the fragment for security reasons. If you think a plugin might include a script for some reason, the call should be changed to $.parseHTML(menuMarkup, document, true).

[csixty4]

Call $.parseHTML instead of $()

[SergeyBiryukov]

Custom fields are also affected: ticket:22975:17.

[ocean90]

jQuery 1.10.0 (#24426) has relaxed the HTML parsing, means it supports a leading whitespace again. But:

We still strongly advise that you use $.parseHTML() when parsing HTML obtained from external sources, and may be making further changes to HTML parsing in the future.

​http://blog.jquery.com/2013/05/24/jquery-1-10-0-and-2-0-1-released/

[ocean90]

23681.patch​ calls $.parseHTML on custom fields too. Here we get an array with two DOM nodes, the first one is an empty line, means text. So we have to pass the second index to jQuery.

[SergeyBiryukov]

Perhaps $.trim() would be faster (suggested in ticket:22975:21)?

[SergeyBiryukov]

FWIW, custom fields work fine in trunk, see ticket:22975:30.

[ocean90]

Replying to SergeyBiryukov:

FWIW, custom fields work fine in trunk, see ticket:22975:30.

Yes, but you don't know how long, see comment:3. $.trim() is a good idea. Testing.

[ocean90]

With $.trim()

[nacin]

This good to go? We can always just wait until 3.7, as 3.6.x will be shipping with 1.10.x.

[wonderboymusic]

these are all marked 3.7-early

[nacin]

ocean90, please commit this if it should be, or close this if it should not.

[ocean90]

In 25546:

Trim leading whitespace from AJAX responses.

This fixes the warning "$(html) HTML strings must start with '<' character" by jQuery Migrate when adding nav menu items, post custom fields or comment replies.

fixes #23681.