feat(kitify): Add assign utility and tests (#10)

libs/kitify/config.mjs

@@ -13,6 +13,11 @@ export default {
 			input: 'src/type/isType.ts',
 			name: 'isType',
 		},
+		//==> object
+		{
+			input: 'src/object/assign.ts',
+			name: 'assign',
+		},
 		//==> dom
 		{
 			input: 'src/dom/detectMouseDirection.ts',

libs/kitify/src/object/__tests__/assign.test.ts

@@ -0,0 +1,38 @@
+import assign from '../assign'
+
+describe('assign()', () => {
+	it('should return an object', () => {
+		expect(assign({}, {})).toEqual({})
+		expect(assign({}, {}, {})).toEqual({})
+	})
+
+	it('should return an object with properties from all input objects', () => {
+		const target = { a: 1 }
+		const source1 = { b: 2 }
+		const source2 = { c: 3 }
+		const result = assign(target, source1, source2)
+		expect(result).toEqual({ a: 1, b: 2, c: 3 })
+	})
+
+	it('should overwrite properties in target object with properties from input objects', () => {
+		const target = { a: 1, b: 2 }
+		const source1 = { b: 3, c: 4 }
+		const source2 = { c: 5 }
+		const result = assign(target, source1, source2)
+		expect(result).toEqual({ a: 1, b: 3, c: 5 })
+	})
+
+	it('should throw an error if target input is undefined or null', () => {
+		expect(() => assign(undefined as any, { a: 1 })).toThrow(TypeError)
+		expect(() => assign(null as any, { a: 1 })).toThrow(TypeError)
+	})
+
+	it('should change source object or not', () => {
+		const target = {}
+		const source1 = { a: 1 }
+		expect(assign(target, source1) === target).toBe(true)
+		expect(assign({}, target, source1) === target).toBe(false)
+		expect(assign(target, source1) === source1).toBe(false)
+		expect(assign(target, source1)).toEqual(source1)
+	})
+})

libs/kitify/src/object/assign.ts

@@ -0,0 +1,20 @@
+interface Assign {
+	<T extends {}, U>(target: T, source: U): T & U
+	<T extends {}, U, V>(target: T, source1: U, source2: V): T & U & V
+	<T extends {}, U, V, W>(target: T, source1: U, source2: V, source3: W): T & U & V & W
+}
+
+const assign: Assign =
+	Object.assign ||
+	function (target: Record<keyof any, any>, ...sources: any[]) {
+		for (let i = 1, len = sources.length; i < len; i++) {
+			const source = sources[i]
+			for (const key in source) {
+				if (Object.prototype.hasOwnProperty.call(source, key)) {
+					target[key] = source[key]
+				}
+			}
+		}
+	}
+
+export default assign