錯誤打字稿與異步迭代目標ES5並在瀏覽器

Question

繼the docs爲「生成和迭代ES5」跑的時候，我增加了以下填充工具：

(Symbol as any).asyncIterator = Symbol.asyncIterator || Symbol.for("Symbol.asyncIterator"); 

這導致我的瀏覽器引發錯誤：

Uncaught TypeError: Cannot assign to read only property ‘asyncIterator’ of function ‘function Symbol() { [native code] }’ 

Answer 1

由於屬性是隻讀，只分配它，當它不存在：

if (typeof (Symbol as any).asyncIterator === 'undefined') { 
(Symbol as any).asyncIterator = Symbol.asyncIterator || Symbol('asyncIterator'); 
}