fix: move sources length check to create-merger

src/index.ts

@@ -8,4 +8,5 @@
 export * from './constants';
 export * from './module';
 export * from './utils';
+export * from './presets';
 export * from './type';

src/module.ts

@@ -29,10 +29,6 @@ function baseMerger<B extends MergerSource[]>(
     options: Options,
     ...sources: B
 ) : MergerResult<B> {
-    if (!sources.length) {
-        throw new SyntaxError('At least one input element is required.');
-    }
-
     let target : MergerSourceUnwrap<B>;
     let source : MergerSourceUnwrap<B> | undefined;
     if (options.priority === PriorityName.RIGHT) {
@@ -159,6 +155,10 @@ export function createMerger(input?: OptionsInput) : Merger {
     return <B extends MergerSource[]>(
         ...sources: B
     ) : MergerResult<B> => {
+        if (!sources.length) {
+            throw new SyntaxError('At least one input element is required.');
+        }
+
         if (options.clone) {
             return baseMerger(options, ...clone(sources));
         }
@@ -182,14 +182,3 @@ export function createMerger(input?: OptionsInput) : Merger {
 }
 
 export const merge = createMerger();
-
-export function assign<A extends Record<string, any>, B extends Record<string, any>[]>(
-    target: A,
-    ...sources: B
-) : A & MergerResult<B> {
-    return createMerger({
-        inPlace: true,
-        priority: 'left',
-        array: false,
-    })(target, ...sources) as A & MergerResult<B>;
-}

src/presets.ts

@@ -0,0 +1,26 @@
+/*
+ * Copyright (c) 2023.
+ * Author Peter Placzek (tada5hi)
+ * For the full copyright and license information,
+ * view the LICENSE file that was distributed with this source code.
+ */
+
+import { createMerger } from './module';
+import type { MergerResult } from './type';
+
+/**
+ * Assign source attributes to a target object.
+ *
+ * @param target
+ * @param sources
+ */
+export function assign<A extends Record<string, any>, B extends Record<string, any>[]>(
+    target: A,
+    ...sources: B
+) : A & MergerResult<B> {
+    return createMerger({
+        inPlace: true,
+        priority: 'left',
+        array: false,
+    })(target, ...sources) as A & MergerResult<B>;
+}

src/utils/clone.ts

@@ -30,18 +30,22 @@ const gT = (() => {
     throw new Error('unable to locate global object');
 })();
 
+/* istanbul ignore next */
 export function clone<T>(value: T) : T {
     if (gT.structuredClone) {
         return gT.structuredClone(value);
     }
 
+    /* istanbul ignore next */
     if (isObject(value)) {
         return { ...value };
     }
 
+    /* istanbul ignore next */
     if (Array.isArray(value)) {
         return [...value] as T;
     }
 
+    /* istanbul ignore next */
     return value;
 }

test/unit/module.spec.ts

@@ -308,4 +308,8 @@ describe('src/module/*.ts', () => {
 
         expect(xB).toEqual(['baz', 'bar']);
     });
+
+    it('should throw error when input source is missing', () => {
+        expect(merge).toThrow(SyntaxError);
+    });
 })

test/unit/presets.spec.ts

@@ -0,0 +1,22 @@
+/*
+ * Copyright (c) 2023.
+ * Author Peter Placzek (tada5hi)
+ * For the full copyright and license information,
+ * view the LICENSE file that was distributed with this source code.
+ */
+
+import {assign} from "../../src";
+
+describe('src/presets', () => {
+    it('should assign default properties', () => {
+        let target = {
+            foo: 'bar'
+        };
+
+        assign(target, {
+            baz: 'boz'
+        });
+
+        expect(target).toEqual({foo: 'bar', baz: 'boz'})
+    })
+})