Using Generators with the for...of loop in Typescript

I am currently facing an issue with Typescript when trying to compile a generator-loop that works perfectly in a modern browser. The code snippet in question is:

/** Should print "x= 1 y= 2" **/
function* gen() { yield [1, 2] }
for (const [x, y] of gen()) { console.log("x=", x, "y=", y) }

Upon running this code through Typescript, it fails to execute as expected. By inputting the code into the Typescript Playground, I was able to observe that the for-of loop gets converted to an array iteration loop, whereas the generator function returns an object.

This seems like an issue with Typescript. Is anyone else experiencing this problem? I couldn't find any information related to this on https://github.com/Microsoft/TypeScript.

What would be the best workaround for this situation? Would using Array.from on the generator function be the most appropriate solution?

typescriptecmascript-6

Answer №1

You're absolutely right, the issue arises from the fact that the for of loop is being converted into a basic array loop in the es5/es3 target.

If you include "downlevelIteration": true in your tsconfig.json, it should resolve the issue, resulting in a completely different code structure.

However, keep in mind that using downlevel iteration for other for of loops with plain arrays may lead to a slight decrease in performance. (Read more about this hidden feature here.)

I also recommend diving into this article, especially the section on 'Reducing Code Size with --importHelpers and tslib'.

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