ExtJS 中组件被销毁后引用变量会发生什么？

Question

ExtJS 新手。我有以下代码。

var comp;
console.log('comp is - ' + comp);
comp = Ext.create('Ext.Component', {
    listeners : {
        beforedestroy : function(comp) {
            console.log('beforedestroy .. ');
        },
        destroy : function(comp) {
            console.log('destroy .. ');
        }
    }
});
console.log('comp is - ' + comp);
console.log('comp id is - ' + comp.getId());
comp.destroy();
console.log('comp is - ' + comp);
console.log('comp id is - ' + comp.getId());

chrome 的控制台输出是

comp is - undefined
comp is - [object Object]
comp id is - component-1009
beforedestroy .. 
destroy .. 
comp is - [object Object]
comp id is - component-1009

看起来即使在组件被销毁之后，变量仍然保留对原始组件的引用。我期望变量在销毁后具有未定义或 null 的值。这是正常行为吗？

Answer 1

Ext-JS 不可能取消对现有组件的引用，因为 JavaScript 没有类似 C++ 的引用。

例如：

var a = {b:2};
var b = a;  
// a and b both reference `{b:2}`, there is nothing you can do 
// to `{b:2}` that would change a or b to be null

您可以使用未记录的属性检查组件是否已被销毁isDestroyed。

comp.isDestroyed // true

您还会注意到该组件已从注册表中删除

Ext.getCmp(comp.id); // undefined