GWT应用程序中使用的Javascript通用clone()方法 [英] Javascript generic clone() method used in GWT application
问题描述
我试图编写一个通用的克隆函数,它应该能够进行真正的深度克隆。我遇到了这个链接,如何深入克隆在JavaScript 并采取功能从那里。
当我尝试使用直接Javascript时,该代码工作得很好。我在代码中做了小的修改,并尝试在GWT中放入JSNI代码。
克隆功能:
deepCopy = function(item)
{
if(!item){
return item;
} // null,未定义值检查
var types = [Number,String,Boolean],result;
//如果有人做了新的String('aaa')或新的Number('444'),则规范原语。
types.forEach(function(type){
if(item instanceof type){
result = type(item);
}
});
if(typeof result ==undefined){
alert(Object.prototype.toString.call(item));
alert(item);
alert(typeof item);
if(Object.prototype.toString.call(item)===[object GWTJavaObject]){
alert('1st');
result = [];
alert('2nd');
item.forEach(function(child,index,array){//抛出的异常
alert('inside for each');
result [index] = deepCopy(child);
});
} else if(typeof item ==GWTJavaObject){
alert('3rd');
if(item.nodeType&& typeof item.cloneNode ==function){
var result = item.cloneNode(true);
} else if(!item.prototype){
result = {};
for(var i in item){
result [i] = deepCopy(item [i]);
}
} else {
if(false&& item.constructor){
result = new item.constructor();
} else {
result = item;
}
}
} else {
alert('4th');
result = item;
}
}
返回结果;
}
传递给此函数的列表如下所示:
列表<整数> list = new ArrayList< Integer>();
list.add(new Integer(100));
list.add(new Integer(200));
list.add(new Integer(300));
列表<整数> newList =(List< Integer>)new Attempt()。clone(list);
整数temp =新整数(500);
list.add(temp);
if(newList.contains(temp))
Window.alert(fail);
else
Window.alert(success);
但是当我执行此操作时,我立即在克隆函数中得到空指针异常 alert(2nd)
行。
请帮忙。
PS:我想在这里得到一个可用于克隆任何对象的通用克隆方法。
GWT原型对象没有forEach方法;它们不会继承标准的JavaScript对象原型,因为它们应该像Java对象那样操作,而不是JavaScript对象。
你可能会抛弃Object.prototype.forEach。 call(item,function(){})
I was trying to write a generic clone function which should be able to do true deep cloning. I have come across this link, How to Deep clone in javascript and took the function from there.
That code workds pretty well when I try using direct Javascript. I did minor modifications in the code and tried to put in the JSNI code in GWT.
clone function:
deepCopy = function(item)
{
if (!item) {
return item;
} // null, undefined values check
var types = [ Number, String, Boolean ], result;
// normalizing primitives if someone did new String('aaa'), or new Number('444');
types.forEach(function(type) {
if (item instanceof type) {
result = type(item);
}
});
if (typeof result == "undefined") {
alert(Object.prototype.toString.call(item));
alert(item);
alert(typeof item);
if (Object.prototype.toString.call(item) === "[object GWTJavaObject]") {
alert('1st');
result = [];
alert('2nd');
item.forEach(function(child, index, array) {//exception thrown here
alert('inside for each');
result[index] = deepCopy(child);
});
} else if (typeof item == "GWTJavaObject") {
alert('3rd');
if (item.nodeType && typeof item.cloneNode == "function") {
var result = item.cloneNode(true);
} else if (!item.prototype) {
result = {};
for ( var i in item) {
result[i] = deepCopy(item[i]);
}
} else {
if (false && item.constructor) {
result = new item.constructor();
} else {
result = item;
}
}
} else {
alert('4th');
result = item;
}
}
return result;
}
And the list am passing to this function is like this:
List<Integer> list = new ArrayList<Integer>();
list.add( new Integer( 100 ) );
list.add( new Integer( 200 ) );
list.add( new Integer( 300 ) );
List<Integer> newList = ( List<Integer> ) new Attempt().clone( list );
Integer temp = new Integer( 500 );
list.add( temp );
if ( newList.contains( temp ) )
Window.alert( "fail" );
else
Window.alert( "success" );
But when I execute this, I get null pointer exception in the clone function immediately after alert("2nd")
line.
Kindly help.
P.S: I am trying to get a generic clone method here that can be used to clone any object.
GWT prototyped objects don't have a forEach method; they do not inherit standard javascript object prototypes, as they are supposed to act like java objects, not javascript objects.
You could probably get away with Object.prototype.forEach.call(item, function(){})
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