add object-key-by-value

README.md

@@ -17,6 +17,10 @@ objectByKeys([1, 2, 3], (key) => Number(key) * 10)
 
 # Development
 ```sh
+$ code src/new-function.ts # add function
+$ code src/new-function.test.ts # add test
+$ code main.ts # add export
+
 $ deno task dev
 ```
 

main.ts

@@ -5,6 +5,7 @@ export * from './src/is-number.ts'
 export * from './src/nameof.ts'
 export * from './src/object-by-keys.ts'
 export * from './src/object-keys.ts'
+export * from './src/object-key-by-value.ts'
 export * from './src/objects-2-object.ts'
 export * from './src/object-swap.ts'
 export * from './src/percent-weighted-avg.ts'

src/object-key-by-value.test.ts

@@ -0,0 +1,22 @@
+import { assertEquals } from 'https://deno.land/std@0.186.0/testing/asserts.ts'
+import { objectKeyByValue } from './object-key-by-value.ts'
+
+Deno.test('object-key-by-value', async test => {
+  await test.step('case of undefined', () => {
+    const obj = { one: 1 }
+
+    assertEquals(
+      objectKeyByValue(obj, 2),
+      undefined,
+    )
+  })
+
+  await test.step('case of exists', () => {
+    const obj = { one: 1 }
+
+    assertEquals(
+      objectKeyByValue(obj, 1),
+      'one',
+    )
+  })
+})

src/object-key-by-value.ts

@@ -0,0 +1,13 @@
+import { objectKeys } from './object-keys.ts'
+
+/**
+ * @example
+ * const obj = { one: 1 }
+ * const key = objectKeyByValue(obj, 1) // 'one' | undefined
+ */
+export const objectKeyByValue = <
+  T extends Record<PropertyKey, U>,
+  U = unknown
+>(object: T, value: U) => {
+  return objectKeys(object).find(key => object[key] === value)
+}