Javascript Object Literals and jQuery
Question
I've updated the script here to give a better example. For $header I've got an anonymous function now returning $("#header") . Although this works I'm sure its not efficient as it calls $header every time it's used - so its the same as just using $("#header") throughout the code.
What I really want is to store $("header") in a variable. When I try to do this with $header2 (below) it fails. #header is red not blue.
When I use firebug to output lib.page.$header2.selector is correctly displays #header . As you can see the script which calls lib.page.init is at the bottom of the DOM.
Any ideas?
<script type="text/javascript">
var lib = {
page : {
$header : function() { return $("#header")},
$header2 : $("#header"),
init: function() {
lib.page.$header().css("background","red");
lib.page.$header2.css("background","blue");
console.log(lib.page.$header2.selector);
}
}
}
</script>
</head>
<body>
<div id="wrapper">
<div id="header">
<em>Example!</em>
</div>
</div>
<script type="text/javascript">
$(function() { lib.page.init(); });
</script>
</body>
2 answers
solution1
2 2010-09-02 20:23:01
Because when you define $header : $('#header') that element is not available? and when you call lib.page.init it is? I am not sure when you call lib.page.init , but I bet it's in $(document).ready() right? And you define the object literal before the dom is ready.
Ok, your div#header is not available by the time you want to assign it to $header, you have two options and I will show you the best option first. It's what I meant with 'put all scripts at the bottom'!
<head>
<!-- dont put scripts here if you can avoid it, it's bad! -->
</head>
<body>
<div id="wrapper">
<div id="header">
<em>Example!</em>
</div>
</div>
<!-- keep scripts at the end of the page just before the </body> tag -->
<script type="text/javascript">
var lib = {
page : {
// div#header is available
$header : $("#header"),
init: function() {
lib.page.$header().css("background","red");
}
}
}
// you don't need onDomReady anymore.
lib.page.init();
</script>
</body>
Another option if you want to keep scripts in the header, is to assign $header in your onDomReady call.
<script>
// create lib etc here
$(function(){ // this is an onDomReady call in jQuery
lib.page.$header = $('#header');
lib.page.init();
});
</script>
solution2
1 ACCPTED 2010-09-07 00:20:47
“发生这种情况是因为在解释脚本时实例化了变量。因此，在解析器进入脚本时，$（“＃header”）不在DOM中。”
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