使用Async Iteration在TypeScript中定位ES5并在浏览器上运行时出错

Question

关于ES4＆＃34;的＆＃34;生成和迭代the docs后，我添加了以下polyfill：

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

这会导致我的浏览器抛出错误：

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

Answer 1

由于该属性是只读的，因此只有在它不存在时才分配：

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