chore(lint): add lint plugin for using for loop instead of `for...o…

…f` over array (#587)

* Add prefer for loop

* change plugin name

* Revert tsconfig

* Revert random comment

* Revert eslint config parser options

---------

Co-authored-by: Sojin Park <[email protected]>

eslint.config.mjs

@@ -4,6 +4,7 @@ import tseslint from 'typescript-eslint';
 import jsdoc from 'eslint-plugin-jsdoc';
 import prettier from 'eslint-config-prettier';
 import pluginVue from 'eslint-plugin-vue';
+import noForOfArrayPlugin from 'eslint-plugin-no-for-of-array';
 
 export default [
   {
@@ -27,7 +28,6 @@ export default [
         ...globals['shared-node-browser'],
         ...globals.es2015,
       },
-
       parserOptions: {
         ecmaFeatures: {
           jsx: true,
@@ -42,6 +42,26 @@ export default [
   prettier,
   jsdoc.configs['flat/recommended'],
   ...pluginVue.configs['flat/recommended'],
+  {
+    files: ['src/**/*.ts'],
+    ignores: ['**/*.spec.ts'],
+    languageOptions: {
+      parser: tseslint.parser,
+      parserOptions: {
+        project: './tsconfig.json',
+        tsconfigRootDir: import.meta.dirname,
+        ecmaFeatures: {
+          jsx: true,
+        },
+      },
+    },
+    plugins: {
+      'no-for-of-array': noForOfArrayPlugin,
+    },
+    rules: {
+      'no-for-of-array/no-for-of-array': 'error',
+    },
+  },
   {
     rules: {
       'no-implicit-coercion': 'error',

package.json

@@ -147,6 +147,7 @@
     "eslint": "^9.9.0",
     "eslint-config-prettier": "^9.1.0",
     "eslint-plugin-jsdoc": "^50.2.2",
+    "eslint-plugin-no-for-of-array": "^0.0.1",
     "eslint-plugin-vue": "^9.28.0",
     "execa": "^9.3.0",
     "globals": "^15.9.0",

src/array/compact.ts

@@ -14,7 +14,8 @@ type NotFalsey<T> = Exclude<T, false | null | 0 | 0n | '' | undefined>;
 export function compact<T>(arr: readonly T[]): Array<NotFalsey<T>> {
   const result: Array<NotFalsey<T>> = [];
 
-  for (const item of arr) {
+  for (let i = 0; i < arr.length; i++) {
+    const item = arr[i];
     if (item) {
       result.push(item as NotFalsey<T>);
     }

src/array/countBy.ts

@@ -28,7 +28,8 @@
 export function countBy<T, K extends PropertyKey>(arr: readonly T[], mapper: (item: T) => K): Record<K, number> {
   const result = {} as Record<K, number>;
 
-  for (const item of arr) {
+  for (let i = 0; i < arr.length; i++) {
+    const item = arr[i];
     const key = mapper(item);
 
     result[key] = (result[key] ?? 0) + 1;

src/array/groupBy.ts

@@ -33,7 +33,8 @@
 export function groupBy<T, K extends PropertyKey>(arr: readonly T[], getKeyFromItem: (item: T) => K): Record<K, T[]> {
   const result = Object.create(null) as Record<K, T[]>;
 
-  for (const item of arr) {
+  for (let i = 0; i < arr.length; i++) {
+    const item = arr[i];
     const key = getKeyFromItem(item);
 
     if (result[key] == null) {

src/array/keyBy.ts

@@ -28,7 +28,8 @@
 export function keyBy<T, K extends PropertyKey>(arr: readonly T[], getKeyFromItem: (item: T) => K): Record<K, T> {
   const result = {} as Record<K, T>;
 
-  for (const item of arr) {
+  for (let i = 0; i < arr.length; i++) {
+    const item = arr[i];
     const key = getKeyFromItem(item);
     result[key] = item;
   }

src/array/maxBy.ts

@@ -64,7 +64,8 @@ export function maxBy<T>(items: readonly T[], getValue: (element: T) => number):
   let maxElement = items[0];
   let max = -Infinity;
 
-  for (const element of items) {
+  for (let i = 0; i < items.length; i++) {
+    const element = items[i];
     const value = getValue(element);
     if (value > max) {
       max = value;

src/array/minBy.ts

@@ -64,7 +64,8 @@ export function minBy<T>(items: readonly T[], getValue: (element: T) => number):
   let minElement = items[0];
   let min = Infinity;
 
-  for (const element of items) {
+  for (let i = 0; i < items.length; i++) {
+    const element = items[i];
     const value = getValue(element);
     if (value < min) {
       min = value;

src/array/partition.ts

@@ -24,7 +24,8 @@ export function partition<T>(arr: readonly T[], isInTruthy: (value: T) => boolea
   const truthy: T[] = [];
   const falsy: T[] = [];
 
-  for (const item of arr) {
+  for (let i = 0; i < arr.length; i++) {
+    const item = arr[i];
     if (isInTruthy(item)) {
       truthy.push(item);
     } else {

src/array/takeWhile.ts

@@ -19,7 +19,8 @@
 export function takeWhile<T>(arr: readonly T[], shouldContinueTaking: (element: T) => boolean): T[] {
   const result: T[] = [];
 
-  for (const item of arr) {
+  for (let i = 0; i < arr.length; i++) {
+    const item = arr[i];
     if (!shouldContinueTaking(item)) {
       break;
     }

src/array/unionBy.ts

@@ -23,7 +23,9 @@
 export function unionBy<T, U>(arr1: readonly T[], arr2: readonly T[], mapper: (item: T) => U): T[] {
   const map = new Map<U, T>();
 
-  for (const item of [...arr1, ...arr2]) {
+  const items = [...arr1, ...arr2];
+  for (let i = 0; i < items.length; i++) {
+    const item = items[i];
     const key = mapper(item);
 
     if (!map.has(key)) {

src/array/uniqBy.ts

@@ -27,7 +27,8 @@
 export function uniqBy<T, U>(arr: readonly T[], mapper: (item: T) => U): T[] {
   const map = new Map<U, T>();
 
-  for (const item of arr) {
+  for (let i = 0; i < arr.length; i++) {
+    const item = arr[i];
     const key = mapper(item);
 
     if (!map.has(key)) {

src/array/uniqWith.ts

@@ -16,7 +16,8 @@
 export function uniqWith<T>(arr: readonly T[], areItemsEqual: (item1: T, item2: T) => boolean): T[] {
   const result: T[] = [];
 
-  for (const item of arr) {
+  for (let i = 0; i < arr.length; i++) {
+    const item = arr[i];
     const isUniq = result.every(v => !areItemsEqual(v, item));
 
     if (isUniq) {

src/compat/function/debounce.spec.ts

@@ -231,7 +231,7 @@ describe('debounce', () => {
     expect(callCount).toBe(2);
   });
 
-  it('subsequent debounced calls return the last `func` result', async done => {
+  it('subsequent debounced calls return the last `func` result', async () => {
     const debounced = debounce(identity, 32);
     debounced('a');
 
@@ -383,7 +383,7 @@ describe('debounce', () => {
     expect(callCount).toBe(2);
   });
 
-  it('should support `maxWait` in a tight loop', async done => {
+  it('should support `maxWait` in a tight loop', async () => {
     const limit = 1000;
     let withCount = 0;
     let withoutCount = 0;
@@ -460,10 +460,12 @@ describe('debounce', () => {
     const object = {};
 
     const debounced = debounce(
-      function (this: any, value: any) {
+      // eslint-disable-next-line @typescript-eslint/no-unused-vars
+      function (this: any, _: any) {
         actual = [this];
+        // eslint-disable-next-line prefer-rest-params
         Array.prototype.push.apply(actual, arguments as any);
-        return ++callCount != 2;
+        return ++callCount !== 2;
       },
       32,
       { leading: true, maxWait: 64 }
@@ -505,7 +507,7 @@ describe('debounce', () => {
     expect(callCount).toBe(isDebounce ? 1 : 2);
   });
 
-  it(`\`_.${methodName}\` should invoke \`func\` with the correct \`this\` binding`, async done => {
+  it(`\`_.${methodName}\` should invoke \`func\` with the correct \`this\` binding`, async () => {
     const actual: any[] = [];
     const object = {
       funced: func(function (this: any) {
@@ -526,8 +528,10 @@ describe('debounce', () => {
     const expected = args.slice();
     const queue: any[] = args.slice();
 
-    var funced = func(function (this: any, _: unknown) {
+    // eslint-disable-next-line @typescript-eslint/no-unused-vars
+    const funced = func(function (this: any, _: unknown) {
       const current = [this];
+      // eslint-disable-next-line prefer-rest-params
       Array.prototype.push.apply(current, arguments as any);
       actual.push(current);
 

src/compat/function/throttle.spec.ts

@@ -39,9 +39,8 @@ describe('throttle', () => {
     expect(results2[0]).not.toStrictEqual(undefined);
   });
 
-  it('should clear timeout when `func` is called', async done => {
+  it('should clear timeout when `func` is called', async () => {
     let callCount = 0;
-    let dateCount = 0;
 
     const throttled = throttle(() => {
       callCount++;
@@ -81,7 +80,7 @@ describe('throttle', () => {
         options
       );
 
-      const start = +new Date();
+      const start = Number(new Date());
       while (Date.now() - start < limit) {
         throttled();
       }
@@ -229,7 +228,7 @@ describe('throttle', () => {
     expect(callCount).toBe(isDebounce ? 1 : 2);
   });
 
-  it(`\`_.${methodName}\` should invoke \`func\` with the correct \`this\` binding`, async done => {
+  it(`\`_.${methodName}\` should invoke \`func\` with the correct \`this\` binding`, async () => {
     const actual: any[] = [];
     const object = {
       funced: func(function (this: any) {
@@ -250,8 +249,10 @@ describe('throttle', () => {
     const expected = args.slice();
     const queue: any[] = args.slice();
 
-    var funced = func(function (this: any, _: unknown) {
+    // eslint-disable-next-line @typescript-eslint/no-unused-vars
+    const funced = func(function (this: any, _: unknown) {
       const current = [this];
+      // eslint-disable-next-line prefer-rest-params
       Array.prototype.push.apply(current, arguments as any);
       actual.push(current);
 

src/compat/math/max.ts

@@ -37,7 +37,8 @@ export function max<T>(items: readonly T[] = []): T | undefined {
   let maxElement = items[0];
   let max: any = undefined;
 
-  for (const element of items) {
+  for (let i = 0; i < items.length; i++) {
+    const element = items[i];
     if (max == null || element > max) {
       max = element;
       maxElement = element;

src/compat/math/min.ts

@@ -41,7 +41,8 @@ export function min<T>(items: readonly T[] = []): T {
   let minElement = items[0];
   let min: any = undefined;
 
-  for (const element of items) {
+  for (let i = 0; i < items.length; i++) {
+    const element = items[i];
     if (min == null || element < min) {
       min = element;
       minElement = element;

src/compat/math/random.ts

@@ -68,9 +68,9 @@ export function random(minimum: number, maximum: number, floating?: boolean): nu
  * const result3 = random(5, 5); // If the minimum is equal to the maximum, an error is thrown.
  */
 export function random(...args: any[]): number {
-  let minimum: number = 0;
-  let maximum: number = 1;
-  let floating: boolean = false;
+  let minimum = 0;
+  let maximum = 1;
+  let floating = false;
 
   switch (args.length) {
     case 1: {
@@ -91,6 +91,7 @@ export function random(...args: any[]): number {
         maximum = args[1];
       }
     }
+    // eslint-disable-next-line no-fallthrough
     case 3: {
       if (typeof args[2] === 'object' && args[2] != null && args[2][args[1]] === args[0]) {
         minimum = 0;

src/compat/object/pick.ts

@@ -94,7 +94,8 @@ export function pick<
 
   const result: any = {};
 
-  for (let keys of keysArr) {
+  for (let i = 0; i < keysArr.length; i++) {
+    let keys = keysArr[i];
     switch (typeof keys) {
       case 'object': {
         if (!Array.isArray(keys)) {

src/compat/predicate/conformsTo.ts

@@ -36,7 +36,9 @@ export function conformsTo(
     return Object.keys(source).length === 0;
   }
 
-  for (const key of Object.keys(source)) {
+  const keys = Object.keys(source);
+  for (let i = 0; i < keys.length; i++) {
+    const key = keys[i];
     const predicate = source[key];
     const value = target[key];
     if ((value === undefined && !(key in target)) || !predicate(value)) {

src/function/debounce.ts

@@ -1,26 +1,3 @@
-interface DebounceTimer {
-  /**
-   * Checks if the timer is active.
-   * @returns {boolean} True if the timer is active, otherwise false.
-   */
-  isActive: () => boolean;
-
-  /**
-   * Triggers the debounce timer.
-   * This method resets the timer and schedules the execution of the debounced function
-   * after the specified delay. If the timer is already active, it clears the existing timeout
-   * before setting a new one.
-   */
-  trigger: () => void;
-
-  /**
-   * Cancels any pending execution of the debounced function.
-   * This method clears the active timer, ensuring that the function will not be called
-   * at the end of the debounce period. It also resets any stored context or arguments.
-   */
-  cancel: () => void;
-}
-
 interface DebounceOptions {
   /**
    * An optional AbortSignal to cancel the debounced function.
@@ -158,6 +135,7 @@ export function debounce<F extends (...args: any[]) => void>(
       return;
     }
 
+    // eslint-disable-next-line @typescript-eslint/no-this-alias
     pendingThis = this;
     pendingArgs = args;
 

src/object/omit.ts

@@ -18,7 +18,8 @@
 export function omit<T extends Record<string, any>, K extends keyof T>(obj: T, keys: readonly K[]): Omit<T, K> {
   const result = { ...obj };
 
-  for (const key of keys) {
+  for (let i = 0; i < keys.length; i++) {
+    const key = keys[i];
     delete result[key];
   }
 

src/object/omitBy.ts

@@ -23,12 +23,12 @@ export function omitBy<T extends Record<string, any>>(
 ): Partial<T> {
   const result: Partial<T> = {};
 
-  for (const [key, value] of Object.entries(obj)) {
-    if (shouldOmit(value, key)) {
-      continue;
+  const objEntries = Object.entries(obj);
+  for (let i = 0; i < objEntries.length; i++) {
+    const [key, value] = objEntries[i];
+    if (!shouldOmit(value, key)) {
+      (result as any)[key] = value;
     }
-
-    (result as any)[key] = value;
   }
 
   return result;

src/object/pick.ts

@@ -18,7 +18,8 @@
 export function pick<T extends Record<string, any>, K extends keyof T>(obj: T, keys: readonly K[]): Pick<T, K> {
   const result = {} as Pick<T, K>;
 
-  for (const key of keys) {
+  for (let i = 0; i < keys.length; i++) {
+    const key = keys[i];
     result[key] = obj[key];
   }