Add getOwn utility function

ts/components/emoji/lib.ts

@@ -20,6 +20,7 @@ import {
 import Fuse from 'fuse.js';
 import PQueue from 'p-queue';
 import is from '@sindresorhus/is';
+import { getOwn } from '../../util/getOwn';
 
 export const skinTones = ['1F3FB', '1F3FC', '1F3FD', '1F3FE', '1F3FF'];
 
@@ -282,19 +283,11 @@ export function convertShortName(
 }
 
 export function emojiToImage(emoji: string): string | undefined {
-  if (!Object.prototype.hasOwnProperty.call(imageByEmoji, emoji)) {
-    return undefined;
-  }
-
-  return imageByEmoji[emoji];
+  return getOwn(imageByEmoji, emoji);
 }
 
 export function emojiToData(emoji: string): EmojiData | undefined {
-  if (!Object.prototype.hasOwnProperty.call(dataByEmoji, emoji)) {
-    return undefined;
-  }
-
-  return dataByEmoji[emoji];
+  return getOwn(dataByEmoji, emoji);
 }
 
 function getCountOfAllMatches(str: string, regex: RegExp) {

ts/test/util/getOwn_test.ts

@@ -0,0 +1,50 @@
+// Copyright 2020 Signal Messenger, LLC
+// SPDX-License-Identifier: AGPL-3.0-only
+
+import { assert } from 'chai';
+
+import { getOwn } from '../../util/getOwn';
+
+describe('getOwn', () => {
+  class Person {
+    public birthYear: number;
+
+    constructor(birthYear: number) {
+      this.birthYear = birthYear;
+    }
+
+    getAge() {
+      return new Date().getFullYear() - this.birthYear;
+    }
+  }
+
+  it('returns undefined when asking for a non-existent property', () => {
+    const obj: Record<string, number> = { bar: 123 };
+    assert.isUndefined(getOwn(obj, 'foo'));
+  });
+
+  it('returns undefined when asking for a non-own property', () => {
+    const obj: Record<string, number> = { bar: 123 };
+    assert.isUndefined(getOwn(obj, 'hasOwnProperty'));
+
+    const person = new Person(1880);
+    assert.isUndefined(getOwn(person, 'getAge'));
+  });
+
+  it('returns own properties', () => {
+    const obj: Record<string, number> = { foo: 123 };
+    assert.strictEqual(getOwn(obj, 'foo'), 123);
+
+    const person = new Person(1880);
+    assert.strictEqual(getOwn(person, 'birthYear'), 1880);
+  });
+
+  it('works even if `hasOwnProperty` has been overridden for the object', () => {
+    const obj: Record<string, unknown> = {
+      foo: 123,
+      hasOwnProperty: () => true,
+    };
+    assert.strictEqual(getOwn(obj, 'foo'), 123);
+    assert.isUndefined(getOwn(obj, 'bar'));
+  });
+});

ts/util/getOwn.ts

@@ -0,0 +1,13 @@
+// Copyright 2020 Signal Messenger, LLC
+// SPDX-License-Identifier: AGPL-3.0-only
+
+import { has } from 'lodash';
+
+// We want this to work with any object, so we allow `object` here.
+// eslint-disable-next-line @typescript-eslint/ban-types
+export function getOwn<TObject extends object, TKey extends keyof TObject>(
+  obj: TObject,
+  key: TKey
+): TObject[TKey] | undefined {
+  return has(obj, key) ? obj[key] : undefined;
+}