[8.8] [ResponseOps] optimize building ecsFieldMap (elastic#159251) (e…

…lastic#159313)

# Backport

This will backport the following commits from `main` to `8.8`:
- [[ResponseOps] optimize building ecsFieldMap
(elastic#159251)](elastic#159251)

<!--- Backport version: 8.9.7 -->

### Questions ?
Please refer to the [Backport tool
documentation](https://github.com/sqren/backport)

<!--BACKPORT [{"author":{"name":"Patrick
Mueller","email":"[email protected]"},"sourceCommit":{"committedDate":"2023-06-08T14:06:01Z","message":"[ResponseOps]
optimize building ecsFieldMap (elastic#159251)\n\nresolves
https://github.com/elastic/kibana/issues/157772\r\n\r\nPreviously on my
M1 Macbook, the `ecsFieldMap` constant takes about 170\r\nms to be
created. It appears this is another case of `array::reduce()`\r\nand
object spread causing performance issues.\r\n\r\nConverting to
(essentially) a filter and map got the time down to 4
ms.\r\n\r\nSlightly critical even though this is only ever run once -
because it's\r\nrun at startup time, and blocking everything else from
running.\r\n\r\nSee:\r\n\r\n-\r\nhttps://www.richsnapp.com/article/2019/06-09-reduce-spread-anti-pattern\r\n-\r\nhttps://prateeksurana.me/blog/why-using-object-spread-with-reduce-bad-idea/","sha":"6e81ae83bc17b020684e3d206dbb696c225e9d1c","branchLabelMapping":{"^v8.9.0$":"main","^v(\\d+).(\\d+).\\d+$":"$1.$2"}},"sourcePullRequest":{"labels":["Feature:Alerting","release_note:skip","Team:ResponseOps","v8.9.0","v8.8.2"],"number":159251,"url":"https://github.com/elastic/kibana/pull/159251","mergeCommit":{"message":"[ResponseOps]
optimize building ecsFieldMap (elastic#159251)\n\nresolves
https://github.com/elastic/kibana/issues/157772\r\n\r\nPreviously on my
M1 Macbook, the `ecsFieldMap` constant takes about 170\r\nms to be
created. It appears this is another case of `array::reduce()`\r\nand
object spread causing performance issues.\r\n\r\nConverting to
(essentially) a filter and map got the time down to 4
ms.\r\n\r\nSlightly critical even though this is only ever run once -
because it's\r\nrun at startup time, and blocking everything else from
running.\r\n\r\nSee:\r\n\r\n-\r\nhttps://www.richsnapp.com/article/2019/06-09-reduce-spread-anti-pattern\r\n-\r\nhttps://prateeksurana.me/blog/why-using-object-spread-with-reduce-bad-idea/","sha":"6e81ae83bc17b020684e3d206dbb696c225e9d1c"}},"sourceBranch":"main","suggestedTargetBranches":["8.8"],"targetPullRequestStates":[{"branch":"main","label":"v8.9.0","labelRegex":"^v8.9.0$","isSourceBranch":true,"state":"MERGED","url":"https://github.com/elastic/kibana/pull/159251","number":159251,"mergeCommit":{"message":"[ResponseOps]
optimize building ecsFieldMap (elastic#159251)\n\nresolves
https://github.com/elastic/kibana/issues/157772\r\n\r\nPreviously on my
M1 Macbook, the `ecsFieldMap` constant takes about 170\r\nms to be
created. It appears this is another case of `array::reduce()`\r\nand
object spread causing performance issues.\r\n\r\nConverting to
(essentially) a filter and map got the time down to 4
ms.\r\n\r\nSlightly critical even though this is only ever run once -
because it's\r\nrun at startup time, and blocking everything else from
running.\r\n\r\nSee:\r\n\r\n-\r\nhttps://www.richsnapp.com/article/2019/06-09-reduce-spread-anti-pattern\r\n-\r\nhttps://prateeksurana.me/blog/why-using-object-spread-with-reduce-bad-idea/","sha":"6e81ae83bc17b020684e3d206dbb696c225e9d1c"}},{"branch":"8.8","label":"v8.8.2","labelRegex":"^v(\\d+).(\\d+).\\d+$","isSourceBranch":false,"state":"NOT_CREATED"}]}]
BACKPORT-->

Co-authored-by: Patrick Mueller <[email protected]>

packages/kbn-alerts-as-data-utils/src/field_maps/ecs_field_map.ts

@@ -11,25 +11,23 @@ import { EcsMetadata, FieldMap } from './types';
 
 const EXCLUDED_TYPES = ['constant_keyword'];
 
-export const ecsFieldMap: FieldMap = Object.keys(EcsFlat).reduce((acc, currKey) => {
-  const value: EcsMetadata = EcsFlat[currKey as keyof typeof EcsFlat];
-
-  // Exclude excluded types
-  if (EXCLUDED_TYPES.includes(value.type)) {
-    return acc;
-  }
-
-  return {
-    ...acc,
-    [currKey]: {
-      type: value.type,
-      array: value.normalize.includes('array'),
-      required: !!value.required,
-      ...(value.scaling_factor ? { scaling_factor: value.scaling_factor } : {}),
-      ...(value.ignore_above ? { ignore_above: value.ignore_above } : {}),
-      ...(value.multi_fields ? { multi_fields: value.multi_fields } : {}),
-    },
-  };
-}, {});
+export const ecsFieldMap: FieldMap = Object.fromEntries(
+  Object.entries(EcsFlat)
+    .filter(([_, value]) => !EXCLUDED_TYPES.includes(value.type))
+    .map(([key, _]) => {
+      const value: EcsMetadata = EcsFlat[key as keyof typeof EcsFlat];
+      return [
+        key,
+        {
+          type: value.type,
+          array: value.normalize.includes('array'),
+          required: !!value.required,
+          ...(value.scaling_factor ? { scaling_factor: value.scaling_factor } : {}),
+          ...(value.ignore_above ? { ignore_above: value.ignore_above } : {}),
+          ...(value.multi_fields ? { multi_fields: value.multi_fields } : {}),
+        },
+      ];
+    })
+);
 
 export type EcsFieldMap = typeof ecsFieldMap;