浅拷贝深拷贝之jQuery中的$.extend分析
jQuery中的$.extend浅拷贝，拷贝对象A时，对象B将拷贝A的所有字段，如果字段是内存地址，B将拷贝地址，若果字段是基元类型，B将复制其值。它的缺点是如果你改变了对象B所指向的内存地址，你同时也改变了对象A指向这个地址的字段。
jQuery中的$.extend深拷贝，这种方式会完全拷贝所有数据，优点是B与A不会相互依赖（A,B完全脱离关联）， 缺点是拷贝的速度更慢，代价更大。
一.$.extend浅拷贝
$.extend浅拷贝实例一，$.extend(a,b)用法，$.extend浅拷贝拷贝对象A时，对象B将拷贝A的所有字段，如果字段是内存地址，B将拷贝地址，若果字段是基元类型，B将复制其值。
<html>
<head>
</head>
<meta charset="GBK">
<title>StudyDemo01</title>
<script type="text/javascript" src="jquery-1.8.3.js"></script>
<script type="text/javascript">
$(document).ready(function() {
var a = {
name : 'zhangshan',
age : 28,
company : {
name : '腾讯',
address : '深圳',
size : 10000
}
};
var b = {
name : 'lisi',
age : 30,
company : {
name : '阿里巴巴',
address : '杭州'
},
stature : '172cm'
};
var c = $.extend(a,b);
console.log('a:' + JSON.stringify(a));
console.log('b:' + JSON.stringify(b));
console.log('c:' + JSON.stringify(c));
});
</script>
<body>
</body>
</html>运行结果：
a:{"name":"lisi","age":30,"company":{"name":"阿里巴巴","address":"杭州"},"stature":"172cm"}
b:{"name":"lisi","age":30,"company":{"name":"阿里巴巴","address":"杭州"},"stature":"172cm"}
c:{"name":"lisi","age":30,"company":{"name":"阿里巴巴","address":"杭州"},"stature":"172cm"}$.extend浅拷贝实例二，$.extend(a,b)用法，如果你改变了对象B所指向的内存地址，你同时也改变了对象A指向这个地址的字段。
<html>
<head>
</head>
<meta charset="GBK">
<title>StudyDemo02</title>
<script type="text/javascript" src="jquery-1.8.3.js"></script>
<script type="text/javascript">
$(document).ready(function() {
var a = {
name : 'zhangshan',
age : 28,
company : {
name : '腾讯',
address : '深圳',
size : 10000
}
};
var b = {
name : 'lisi',
age : 30,
company : {
name : '阿里巴巴',
address : '杭州'
},
stature : '172cm'
};
var c = $.extend(a,b);
b.name = 'test';
b.company.address = '北京';
console.log('a:' + JSON.stringify(a));
console.log('b:' + JSON.stringify(b));
console.log('c:' + JSON.stringify(c));
});
</script>
<body>
</body>
</html>运行结果：
a:{"name":"lisi","age":30,"company":{"name":"阿里巴巴","address":"北京"},"stature":"172cm"}
b:{"name":"test","age":30,"company":{"name":"阿里巴巴","address":"北京"},"stature":"172cm"}
c:{"name":"lisi","age":30,"company":{"name":"阿里巴巴","address":"北京"},"stature":"172cm"}$.extend浅拷贝实例三，$.extend({},a,b)用法
<html>
<head>
</head>
<meta charset="GBK">
<title>StudyDemo03</title>
<script type="text/javascript" src="jquery-1.8.3.js"></script>
<script type="text/javascript">
$(document).ready(function() {
var a = {
name : 'zhangshan',
age : 28,
company : {
name : '腾讯',
address : '深圳',
size : 10000
}
};
var b = {
name : 'lisi',
age : 30,
company : {
name : '阿里巴巴',
address : '杭州'
},
stature : '172cm'
};
var c = $.extend({},a,b);
console.log('a:' + JSON.stringify(a));
console.log('b:' + JSON.stringify(b));
console.log('c:' + JSON.stringify(c));
});
</script>
<body>
</body>
</html>运行结果：
a:{"name":"zhangshan","age":28,"company":{"name":"腾讯","address":"深圳","size":10000}}
b:{"name":"lisi","age":30,"company":{"name":"阿里巴巴","address":"杭州"},"stature":"172cm"}
c:{"name":"lisi","age":30,"company":{"name":"阿里巴巴","address":"杭州"},"stature":"172cm"}$.extend浅拷贝实例四，$.extend({},a,b)用法
<html>
<head>
</head>
<meta charset="GBK">
<title>StudyDemo04</title>
<script type="text/javascript" src="jquery-1.8.3.js"></script>
<script type="text/javascript">
$(document).ready(function() {
var a = {
name : 'zhangshan',
age : 28,
company : {
name : '腾讯',
address : '深圳',
size : 10000
}
};
var b = {
name : 'lisi',
age : 30,
company : {
name : '阿里巴巴',
address : '杭州'
},
stature : '172cm'
};
var c = $.extend({},a,b);
a.name = 'zhangshan01';
b.name = 'lisi01';
b.company.address = 'shengzhen';
console.log('a:' + JSON.stringify(a));
console.log('b:' + JSON.stringify(b));
console.log('c:' + JSON.stringify(c));
});
</script>
<body>
</body>
</html>运行结果：
a:{"name":"zhangshan01","age":28,"company":{"name":"腾讯","address":"深圳","size":10000}}
b:{"name":"lisi01","age":30,"company":{"name":"阿里巴巴","address":"shengzhen"},"stature":"172cm"}
c:{"name":"lisi","age":30,"company":{"name":"阿里巴巴","address":"shengzhen"},"stature":"172cm"}由$.extend浅拷贝实例三、实例四不难发现，$.extend({},a,b)方法会依次拷贝a、b对象，且b里面的对象是内存地址的拷贝(加上b.company.address = 'shengzhen';语句后执行结果可以看出)。
二.$.extend深拷贝
$.extend深拷贝实例一，$.extend(true,a,b)用法
<html>
<head>
</head>
<meta charset="GBK">
<title>StudyDemo05</title>
<script type="text/javascript" src="jquery-1.8.3.js"></script>
<script type="text/javascript">
$(document).ready(function() {
var a = {
name : 'zhangshan',
age : 28,
company : {
name : '腾讯',
address : '深圳',
size : 10000
}
};
var b = {
name : 'lisi',
age : 30,
company : {
name : '阿里巴巴',
address : '杭州'
},
stature : '172cm'
};
var c = $.extend(true,a,b);
console.log('a:' + JSON.stringify(a));
console.log('b:' + JSON.stringify(b));
console.log('c:' + JSON.stringify(c));
});
</script>
<body>
</body>
</html>运行结果：
a:{"name":"lisi","age":30,"company":{"name":"阿里巴巴","address":"杭州","size":10000},"stature":"172cm"}
b:{"name":"lisi","age":30,"company":{"name":"阿里巴巴","address":"杭州"},"stature":"172cm"}
c:{"name":"lisi","age":30,"company":{"name":"阿里巴巴","address":"杭州","size":10000},"stature":"172cm"}$.extend深拷贝实例二，$.extend(true,a,b)之后，修改b对象
<html>
<head>
</head>
<meta charset="GBK">
<title>StudyDemo06</title>
<script type="text/javascript" src="jquery-1.8.3.js"></script>
<script type="text/javascript">
$(document).ready(function() {
var a = {
name : 'zhangshan',
age : 28,
company : {
name : '腾讯',
address : '深圳',
size : 10000
}
};
var b = {
name : 'lisi',
age : 30,
company : {
name : '阿里巴巴',
address : '杭州'
},
stature : '172cm'
};
var c = $.extend(true,a,b);
b.name = 'test';
b.company.address = '北京';
console.log('a:' + JSON.stringify(a));
console.log('b:' + JSON.stringify(b));
console.log('c:' + JSON.stringify(c));
});
</script>
<body>
</body>
</html>运行结果：
a:{"name":"lisi","age":30,"company":{"name":"阿里巴巴","address":"杭州","size":10000},"stature":"172cm"}
b:{"name":"test","age":30,"company":{"name":"阿里巴巴","address":"北京"},"stature":"172cm"}
c:{"name":"lisi","age":30,"company":{"name":"阿里巴巴","address":"杭州","size":10000},"stature":"172cm"}$.extend深拷贝实例三
<html>
<head>
</head>
<meta charset="GBK">
<title>StudyDemo07</title>
<script type="text/javascript" src="jquery-1.8.3.js"></script>
<script type="text/javascript">
$(document).ready(function() {
var a = {
name : 'zhangshan',
age : 28,
company : {
name : '腾讯',
address : '深圳',
size : 10000
}
};
var b = {
name : 'lisi',
age : 30,
company : {
name : '阿里巴巴',
address : '杭州'
},
stature : '172cm'
};
var c = $.extend(true,{},a,b);
console.log('a:' + JSON.stringify(a));
console.log('b:' + JSON.stringify(b));
console.log('c:' + JSON.stringify(c));
});
</script>
<body>
</body>
</html>运行结果：
a:{"name":"zhangshan","age":28,"company":{"name":"腾讯","address":"深圳","size":10000}}
b:{"name":"lisi","age":30,"company":{"name":"阿里巴巴","address":"杭州"},"stature":"172cm"}
c:{"name":"lisi","age":30,"company":{"name":"阿里巴巴","address":"杭州","size":10000},"stature":"172cm"}$.extend深拷贝实例四，修改b对象
<html>
<head>
</head>
<meta charset="GBK">
<title>StudyDemo08</title>
<script type="text/javascript" src="jquery-1.8.3.js"></script>
<script type="text/javascript">
$(document).ready(function() {
var a = {
name : 'zhangshan',
age : 28,
company : {
name : '腾讯',
address : '深圳',
size : 10000
}
};
var b = {
name : 'lisi',
age : 30,
company : {
name : '阿里巴巴',
address : '杭州'
},
stature : '172cm'
};
var c = $.extend(true,{},a,b);
a.name = 'zhangshan01';
b.name = 'lisi01';
b.company.address = 'shengzhen';
console.log('a:' + JSON.stringify(a));
console.log('b:' + JSON.stringify(b));
console.log('c:' + JSON.stringify(c));
});
</script>
<body>
</body>
</html>运行结果：
a:{"name":"zhangshan01","age":28,"company":{"name":"腾讯","address":"深圳","size":10000}}
b:{"name":"lisi01","age":30,"company":{"name":"阿里巴巴","address":"shengzhen"},"stature":"172cm"}
c:{"name":"lisi","age":30,"company":{"name":"阿里巴巴","address":"杭州","size":10000},"stature":"172cm"}三.$.extend源代码
查看分析$.extend源代码，我们就不难理解上面实例的运行结果了
jQuery.extend = jQuery.fn.extend = function() {
var options, name, src, copy, copyIsArray, clone,
target = arguments[0] || {},
i = 1,
length = arguments.length,
deep = false;
// Handle a deep copy situation
if ( typeof target === "boolean" ) {
deep = target;
target = arguments[1] || {};
// skip the boolean and the target
i = 2;
}
// Handle case when target is a string or something (possible in deep copy)
if ( typeof target !== "object" && !jQuery.isFunction(target) ) {
target = {};
}
// extend jQuery itself if only one argument is passed
if ( length === i ) {
target = this;
--i;
}
for ( ; i < length; i++ ) {
// Only deal with non-null/undefined values
if ( (options = arguments[ i ]) != null ) {
// Extend the base object
for ( name in options ) {
src = target[ name ];
copy = options[ name ];
// Prevent never-ending loop
if ( target === copy ) {
continue;
}
// Recurse if we're merging plain objects or arrays
if ( deep && copy && ( jQuery.isPlainObject(copy) || (copyIsArray = jQuery.isArray(copy)) ) ) {
if ( copyIsArray ) {
copyIsArray = false;
clone = src && jQuery.isArray(src) ? src : [];
} else {
clone = src && jQuery.isPlainObject(src) ? src : {};
}
// Never move original objects, clone them
target[ name ] = jQuery.extend( deep, clone, copy );
// Don't bring in undefined values
} else if ( copy !== undefined ) {
target[ name ] = copy;
}
}
}
}
// Return the modified object
return target;
};