Error when targeting ES5 in TypeScript with Async Iteration and running on the browser

Question

Following the docs for "Generation and Iteration for ES5", I added the following polyfill:

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

This causes my browser to throw an error:

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

Wex · Accepted Answer · 2017-09-08 19:03:26Z

2

Since the property is readonly, only assign it when it doesn't exist:

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

answered Sep 8, 2017 at 19:03

Wex

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