$extend()

$extend({dest,src1,src2}); 将src1,src2合并到dest中 
$extend({{},src1,src2}); 将src1,src2合并后返回 
$extend({true,{},src1,src2,src3}); 将src1,src2合并并将子对象合并后返回 

例：var result=$.extend( false, {},  { name: "John", location:{city: "Boston",county:"USA"} },  { last: "Resig", location: {state: "MA",county:"China"} } ); 
那么合并后的结果就是: 
  result={name:"John",last:"Resig",location:{state:"MA",county:"China"}} 

例2： 
var result=$.extend( true,  {},      { name: "John", location: {city: "Boston",county:"USA"} },      { last: "Resig", location: {state: "MA",county:"China"} } ); 

那么合并后的结果就是: 
result={name:"John",last:"Resig",        location:{city:"Boston",state:"MA",county:"China"}}