Remove usage of Array#fill (#20071)

gaearon · web-flow · commit 6f62abb58ae4 · 2020-10-21T13:17:44.000+01:00
diff --git a/packages/react-reconciler/src/ReactFiberLane.js b/packages/react-reconciler/src/ReactFiberLane.js
@@ -640,7 +640,13 @@ export function higherLanePriority(
 }
 
 export function createLaneMap<T>(initial: T): LaneMap<T> {
- return new Array(TotalLanes).fill(initial);
+ // Intentionally pushing one by one.
+ // https://v8.dev/blog/elements-kinds#avoid-creating-holes
+ const laneMap = [];
+ for (let i = 0; i < TotalLanes; i++) {
+ laneMap.push(initial);
+ }
+ return laneMap;
 }
 
 export function markRootUpdated(

Original file line number	Diff line number	Diff line change
`@@ -640,7 +640,13 @@ export function higherLanePriority(`
`640`	`640`	`}`
`641`	`641`
`642`	`642`	`exportfunctioncreateLaneMap<T>(initial: T): LaneMap<T>{`
`643`		`-returnnewArray(TotalLanes).fill(initial);`
	`643`	`+// Intentionally pushing one by one.`
	`644`	`+// https://v8.dev/blog/elements-kinds#avoid-creating-holes`
	`645`	`+constlaneMap=[];`
	`646`	`+for(leti=0;i<TotalLanes;i++){`
	`647`	`+laneMap.push(initial);`
	`648`	`+}`
	`649`	`+ return laneMap;`
`644`	`650`	`}`
`645`	`651`
`646`	`652`	`exportfunctionmarkRootUpdated(`