如何从代理对象获取代理的处理程序? [英] How to get proxy's handler from proxy object?
问题描述
例如,如果我有这个处理程序/代理(来自 MDN示例)...
For example, if I have this handler/proxy (from the MDN example)...
var handler = {
get: function(target, name){
return name in target?
target[name] :
37;
}
};
var p = new Proxy({}, handler);
p.a = 1;
p.b = undefined;
console.log(p.a, p.b); // 1, undefined
console.log('c' in p, p.c); // false, 37
是否可以探测代理, p
,以某种方式允许我返回处理程序
对象。
is it possible to probe the proxy, p
, in some way that allows me to get the handler
object back.
行:
p.__handler__ // returns handler object -> Object {get: handler.get(), set: handler.set(), ...}
p.__handler__.get // returns get prop/fn of handler -> function(target, name){ ...}
显然,各种陷阱设置在处理程序中仍然知道代理,但有一个明确的方式从代理本身返回它们/处理程序?如果是这样,怎么做?
我目前没有具体的用例,但如果你想动态改变,我可以看到它很有用已有代理后的处理程序/陷阱。
I have no specific use-case for this at the moment, but I could see this being useful if you wanted to dynamically change a handler/traps after you already have a proxy.
推荐答案
ECMAScript无法访问内部[[ProxyHandler]]也无法访问[[ProxyTarget]]插槽。
ECMAScript provides no way to access the internal [[ProxyHandler]] nor [[ProxyTarget]] slots.
某些实现可能会提供一些非标准方式,但不要将其视为理所当然。
Some implementations may provide some non-standard ways, but don't take it for granted.
例如,在Firefox特权代码上,您可以使用
For example, on Firefox privileged code, you can know if an object is a proxy using
Components.utils.isProxy(object);
我建议实现类似的方法来公开[[ProxyHandler]]和[[ProxyTarget]]。他们告诉我在 Debugger.Object
而不是 Components.utils
中实现它们。
I proposed implementing similar methods to expose the [[ProxyHandler]] and [[ProxyTarget]]. They told me to implement them in Debugger.Object
instead of Components.utils
.
当补丁登陆时,可以使用类似
When the patch lands, it will be possible to use something like
Components.utils.import('resource://gre/modules/jsdebugger.jsm');
var Cc = Components.classes;
// Add a debugger to a new global
var global = new Components.utils.Sandbox(
Cc["@mozilla.org/systemprincipal;1"].createInstance(Ci.nsIPrincipal),
{ freshZone: true }
);
addDebuggerToGlobal(global);
var dbg = new global.Debugger().addDebuggee(this);
// Create a debugger object of your object, and run proxy getters
var dbgObj = dbg.makeDebuggeeValue(object);
if(dbgObj.isProxy) { // a boolean
dbgObj.proxyHandler.unsafeDereference(); // the [[ProxyHandler]]
dbgObj.proxyTarget.unsafeDereference(); // the [[ProxyTarget]]
}
这篇关于如何从代理对象获取代理的处理程序?的文章就介绍到这了,希望我们推荐的答案对大家有所帮助,也希望大家多多支持IT屋!