ios8.3下面，EventRegister文件代码有bug

var windowKey = Symbol.for("er_register_map");

var registerMap = window[windowKey] = window[windowKey] || {
ids: {}
}
//TypeError: undefined is not an object (evaluating 'hasOwnProperty.call(it, key)')

可以复现：
var a = Symbol('fff')
window[a] = 1 // error
var b = {}
b[a] = 1 //true