feat(mergeProps): add mergeProps function

src/index.ts

@@ -7,3 +7,4 @@ export { default as set, merge, mergeWith } from './utils/set';
 export { default as warning, noteOnce } from './warning';
 export { default as omit } from './omit';
 export { default as toArray } from './Children/toArray';
+export { default as mergeProps } from './mergeProps';

src/mergeProps.ts

@@ -0,0 +1,18 @@
+function mergeProps<A, B>(a: A, b: B): B & A;
+function mergeProps<A, B, C>(a: A, b: B, c: C): C & B & A;
+function mergeProps<A, B, C, D>(a: A, b: B, c: C, d: D): D & C & B & A;
+function mergeProps(...items: any[]) {
+  const ret: any = {};
+  for (const item of items) {
+    if (item) {
+      for (const key of Object.keys(item)) {
+        if (item[key] !== undefined) {
+          ret[key] = item[key];
+        }
+      }
+    }
+  }
+  return ret;
+}
+
+export default mergeProps;

tests/mergeProps.test.ts

@@ -0,0 +1,52 @@
+import mergeProps from '../src/mergeProps';
+
+describe('mergeProps', () => {
+  it('merges two objects with later overriding earlier', () => {
+    const a = { foo: 1, bar: 2 };
+    const b = { bar: 3, baz: 4 };
+    expect(mergeProps(a, b)).toEqual({ foo: 1, bar: 3, baz: 4 });
+  });
+
+  it('excludes keys with undefined values', () => {
+    const a = { foo: 1, bar: undefined };
+    const b = { bar: 2 };
+    expect(mergeProps(a, b)).toEqual({ foo: 1, bar: 2 });
+  });
+
+  it('does not include key if value is undefined in last object', () => {
+    const a = { foo: 1 };
+    const b = { bar: undefined };
+    expect(mergeProps(a, b)).toEqual({ foo: 1 });
+  });
+
+  it('skips null and undefined items', () => {
+    const a = { foo: 1 };
+    expect(mergeProps(a, null as any)).toEqual({ foo: 1 });
+    expect(mergeProps(a, undefined as any)).toEqual({ foo: 1 });
+    expect(mergeProps(null as any, a)).toEqual({ foo: 1 });
+    expect(mergeProps(undefined as any, a)).toEqual({ foo: 1 });
+  });
+
+  it('merges three or more objects with rightmost winning', () => {
+    const a = { a: 1 };
+    const b = { a: 2, b: 2 };
+    const c = { a: 3, b: 3, c: 3 };
+    expect(mergeProps(a, b, c)).toEqual({ a: 3, b: 3, c: 3 });
+  });
+
+  it('returns empty object for no args', () => {
+    expect((mergeProps as (...items: any[]) => any)()).toEqual({});
+  });
+
+  it('returns copy of single object', () => {
+    const a = { foo: 1, bar: 2 };
+    expect((mergeProps as (...items: any[]) => any)(a)).toEqual({
+      foo: 1,
+      bar: 2,
+    });
+  });
+
+  it('handles empty objects', () => {
+    expect(mergeProps({}, { a: 1 }, {})).toEqual({ a: 1 });
+  });
+});