分享50个使你成为高级javascript开发者的jQuery的代码开发技巧 - 第二部分
转自
http://www.gbin1.com/technology/jquery/50jquerycodesnippetsforbetterjavascript2/index.html

26. 显示或者删除输入框的缺省值

//This snippet will show you how to keep a default value
//in a text input field for when a user hasn't entered in
//a value to replace it
swap_val = [];
$(".swap").each(function(i){
    swap_val[i] = $(this).val();
    $(this).focusin(function(){
        if ($(this).val() == swap_val[i]) {
            $(this).val("");
        }
    }).focusout(function(){
        if ($.trim($(this).val()) == "") {
            $(this).val(swap_val[i]);
        }
    });
});
<INPUT class=swap value="Enter Username here.." type=text>
27. 指定时间后自动隐藏或者关闭元素(1.4支持）

//Here's how we used to do it in 1.3.2 using setTimeout
setTimeout(function() {
  $('.mydiv').hide('blind', {}, 500)
}, 5000);
//And here's how you can do it with 1.4 using the delay() feature (this is a lot like sleep)
$(".mydiv").delay(5000).hide('blind', {}, 500);
28. 动态创建元素到DOM

var newgbin1Div = $('');
newgbin1Div.attr('id','gbin1.com').appendTo('body');
29. 限制textarea的字符数量

jQuery.fn.maxLength = function(max){
  this.each(function(){
    var type = this.tagName.toLowerCase();
    var inputType = this.type? this.type.toLowerCase() : null;
    if(type == "input" &amp;&amp; inputType == "text" || inputType == "password"){
      //Apply the standard maxLength
      this.maxLength = max;
    }
    else if(type == "textarea"){
      this.onkeypress = function(e){
        var ob = e || event;
        var keyCode = ob.keyCode;
        var hasSelection = document.selection? document.selection.createRange().text.length &gt; 0 : this.selectionStart != this.selectionEnd;
        return !(this.value.length &gt;= max &amp;&amp; (keyCode &gt; 50 || keyCode == 32 || keyCode == 0 || keyCode == 13) &amp;&amp; !ob.ctrlKey &amp;&amp; !ob.altKey &amp;&amp; !hasSelection);
      };
      this.onkeyup = function(){
        if(this.value.length &gt; max){
          this.value = this.value.substring(0,max);
        }
      };
    }
  });
};
//Usage:
$('#gbin1textarea').maxLength(500);
30. 为函数创建一个基本测试用例

//Separate tests into modules.
module("Module B");
test("some other gbin1.com test", function() {
  //Specify how many assertions are expected to run within a test.
  expect(2);
  //A comparison assertion, equivalent to JUnit's assertEquals.
  equals( true, false, "failing test" );
  equals( true, true, "passing test" );
});
31. 使用jQuery克隆元素

var cloned = $('#gbin1div').clone();
32. 测试一个元素在jQuery中是否可见

if($(element).is(':visible') == 'true') { //The element is Visible }
33. 元素屏幕居中

jQuery.fn.center = function () {
  this.css('position','absolute');