SimpleChanges
用 SimpleChange对象表示的变更的哈希表，这些对象以声明的属性名称存储在指令或组件上，这些属性属于它们。这是传递给 ngOnChanges 钩子的类型。
A hashtable of changes represented by SimpleChangeobjects stored at the declared property name they belong to on a Directive or Component. This is the type passed to the ngOnChanges hook.
interface SimpleChanges {
__index(propName: string): SimpleChange
}
