add pick function

Author: li-jia-nan

src/omit.ts

@@ -1,14 +1,20 @@
-export default function omit<T extends object, K extends keyof T>(
-  obj: T,
+const omit = <T extends object, K extends keyof T>(
+  oriObj: T,
   fields: K[] | readonly K[],
-): Omit<T, K> {
-  const clone = Object.assign({}, obj);
+): Omit<T, K> => {
+  if (!oriObj) {
+    return {} as Omit<T, K>;
+  }
+
+  const clone = Object.assign({}, oriObj);
 
   if (Array.isArray(fields)) {
-    fields.forEach(key => {
+    for (const key in fields) {
       delete clone[key];
-    });
+    }
   }
 
   return clone;
-}
+};
+
+export default omit;

src/pick.ts

@@ -0,0 +1,20 @@
+const pick = <T extends object, K extends keyof T>(
+  oriObj: T,
+  fields: K[] | readonly K[],
+): Pick<T, K> => {
+  if (!oriObj) {
+    return {} as Pick<T, K>;
+  }
+
+  const result = {} as Pick<T, K>;
+
+  if (Array.isArray(fields)) {
+    for (const key of fields) {
+      result[key] = oriObj[key];
+    }
+  }
+
+  return result;
+};
+
+export default pick;

tests/pick.test.ts

@@ -0,0 +1,18 @@
+import pick from '../src/pick';
+
+describe('omit', () => {
+  it('should work', () => {
+    const ret = pick({ a: 1, b: 2, c: 3 }, ['a']);
+    expect(ret).toEqual({ a: 1 });
+  });
+
+  it('invalidate array', () => {
+    const ret = pick({ bamboo: 1 }, null);
+    expect(ret).toEqual({});
+  });
+
+  it('readonly array', () => {
+    const ret = pick({ a: 1, b: 2 }, ['b'] as const);
+    expect(ret).toEqual({ b: 2 });
+  });
+});