jQuery callback after append

问题:

I have the following code:

HTML

<div id="body"></div>

JS

var site = { 'pageData' : [
    {   
        'loadInTo'      :   '#aboutUs',
        'url'           :   'aboutUs.html',
        'urlSection'    :   '.sectionInner'
    },
    {   
        'loadInTo'      :   '#whatWeDo',
        'url'           :   'whatWeDo.html',
        'urlSection'    :   '.sectionInner' 
    },
    {   
        'loadInTo'      :   '#ourValues',
        'url'           :   'ourValues.html',
        'urlSection'    :   '.sectionInner' 
    },
    {   
        'loadInTo'      :   '#ourExpertise',
        'url'           :   'ourExpertise.html',
        'urlSection'    :   '.sectionInner' 
    }   
]}

for(i=0; i < site.pageData.length; i++) {
    var loader = site.pageData[i];

    $('#body').append('<div id="'+ loader.loadInTo +'" class="section" />');
    $(loader.loadInTo).load(loader.url + ' ' + loader.urlSection);      
}

What I am doing is looping through the site variable and writing out some div's using jQuery's append method that have the id set in 'loadInTo', this works fine. After this is complete I want to use jQuery's load method to populate the divs with HTML from other pages. Is there a to make a callback after appending the div's? something like this:

$('#body').append('<div id="'+ loader.loadInTo +'" class="section" />', function(){
        $(loader.loadInTo).load(loader.url + ' ' + loader.urlSection);
    });

回答1:

jQuery doesn't support a callback for .append. Also, it's much more efficient to append the data at once, rather than calling .append for each element. See the code below.

Every element-to-append is added to a string. Once the string has finished, a marker is added, and the HTML is appended. Then, a poller is activated, checking whether the marker element exist in the DOM. If it exists, the poller is cleared, the marker is removed, and the code executes.

Update: .substr(1) is used when the ID is set, because the ID shouldn't be prefixed by #.

var toAppend = '';
var markerID = 'mark-end-of-append' + (new Date).getTime(); //Random
for(var i=0; i<site.pageData.length; i++) {
    var loader = site.pageData[i];
    toAppend += '<div id="'+ loader.loadInTo.substr(1) +'" class="section" />';
}
toAppend += '<div id="' + markerID + '"></div>';
$('#body').append(toAppend);
var poller = window.setInterval(function(){
    var detected = document.getElementById(markerID);
    if(detected){ //DOM is much more efficient
        window.clearInterval(poller);
        $(detected).remove(); //Remove marker
        for(var i=0; i<site.pageData.length; i++){
            var loader = site.pageData[i];
            $(loader.loadInTo).load(loader.url + ' ' + loader.urlSection);
        }
    }
}, 100); //Check 10x per second

回答2:

Why a callback? Is $(...).append() an asynchronous call? I think not, so why not just write another statement?

If what you're after is avoiding code-replication, you may create the new division in a temporary variable:

for( ... ) {
  var loader = ...;
  var newDiv = createDiv( {id:loader.loadInto } );
  $('#body').append( newDiv );
  $(newDiv).load( loader.url + ' ' + loader.urlSection );
}

Where the createDiv function may look like

function createDiv( settings ) {
  document.createElement('div');
  $(div).class("section");
  $(div).id(settings.id);
  return div;
}

回答3:

In jquery you could use $() just after your appending contents code. This way you can be sure that the content is loaded and the DOM is ready before performing any tasks on the appended content.

$(function(){
//code that needs to be executed when DOM is ready, after manipulation
});

$() calls a function that either registers a DOM-ready callback (if a function is passed to it) or returns elements from the DOM (if a selector string or element is passed to it)

You can find more here
difference between $ and $() in jQuery
http://api.jquery.com/ready/