Only use 'es2015.iterable' to avoid accidental es2015 feature usage. #28951

DanielRosenwasser · 2018-12-11T01:50:45Z

j-oliveras · 2018-12-11T07:23:37Z

ajafff · 2018-12-11T09:48:06Z

src/compiler/core.ts

@@ -2165,6 +2165,10 @@ namespace ts {
    }

    export function fill<T>(length: number, cb: (index: number) => T): T[] {
-        return new Array(length).fill(0).map((_, i) => cb(i));
+        const result = Array<T>(length);


At least in V8 this causes the array to be considered "holey" and therefore it's not as optimized as packed arrays.
On the other hand repeatedly calling push needs to grow the backing store.

I'd say this is fine as is, as this function is only used in a single place in generateTypes.ts. So the holey array won't cause too much deoptimization where it's used. The alternative using push wouldn't be a problem either because the arrays are unlikely to contain more than a dozen elements.

DanielRosenwasser and others added 2 commits December 10, 2018 17:46

Only use 'es2015.iterable' to avoid accidental es2015 feature usage.

cc477ee

Don't use 'fill' in 'fill'.

28c3663

DanielRosenwasser force-pushed the fixLibToIterableAndES5 branch from be07efc to 28c3663 Compare December 11, 2018 05:20

ajafff approved these changes Dec 11, 2018

View reviewed changes

DanielRosenwasser merged commit 5ab24ed into master Dec 11, 2018

DanielRosenwasser deleted the fixLibToIterableAndES5 branch January 18, 2020 03:20

Provide feedback

Saved searches

Use saved searches to filter your results more quickly

Only use 'es2015.iterable' to avoid accidental es2015 feature usage. #28951

Only use 'es2015.iterable' to avoid accidental es2015 feature usage. #28951

DanielRosenwasser commented Dec 11, 2018 •

edited

Loading

j-oliveras commented Dec 11, 2018

ajafff Dec 11, 2018

Only use 'es2015.iterable' to avoid accidental es2015 feature usage. #28951

Only use 'es2015.iterable' to avoid accidental es2015 feature usage. #28951

Conversation

DanielRosenwasser commented Dec 11, 2018 • edited Loading

j-oliveras commented Dec 11, 2018

ajafff Dec 11, 2018

Choose a reason for hiding this comment

DanielRosenwasser commented Dec 11, 2018 •

edited

Loading