merge: useFocus 구현 (#28)

* feat: useFocus 기능 구현

* test: useFocus 기능 테스트 추가

* docs: Storybook, README업데이트

* chore: parameter에서 기본값 정의하도록 변경

(#27)

README.md

@@ -204,6 +204,20 @@ You can determine the initial on/off state of the toggle through `defaultValue`.
 
 `toggle` : Reverses the current state of the switch.
 
+### useFocus
+
+Executes the provided callback function when a DOM element becomes visible on the screen.
+
+#### Parameters
+
+`onFocusCallback`: A function to execute when the element comes into focus.
+`threshold`: Determines the visibility threshold for the element. A value of 1 means the element must be fully visible within the viewport.
+`rootMargin`: Adjusts the viewport’s dimensions using the format "top right bottom left", with units explicitly specified.
+
+#### Return Value
+
+`ref`: A ref object to assign to the DOM element that should trigger the focus callback.
+
 ## Animation
 
 The animation of this package is based on ClassName by default.

src/index.ts

@@ -11,6 +11,7 @@ import useDebounce from './useDebounce/useDebounce';
 import useLocalStorage from './useLocalStorage/useLocalStorage';
 import useDisclosure from './useDisclosure/useDisclosure';
 import useModal from './useModal/useModal';
+import useFocus from './useFocus/useFocus';
 
 export {
   useInput,
@@ -26,4 +27,5 @@ export {
   useLocalStorage,
   useDisclosure,
   useModal,
+  useFocus,
 };

src/stories/useFocus/Docs.mdx

@@ -0,0 +1,22 @@
+import { Canvas, Meta, Description } from '@storybook/blocks';
+import * as Focus from './Focus.stories';
+
+<Meta of={Focus} />
+
+# useFocus
+
+DOM Element가 화면에 노출되었을때, callback으로 전달된 함수를 실행합니다.
+
+## 함수인자
+
+`onFocusCallback` : 요소가 focus되었을때, 수행할 함수입니다.
+
+`threshold` : 요소가 화면에 보일때의 기준을 결정합니다. 1이면 전체요소가 모두 화면에 들어왔을때 입니다.
+
+`rootMargin` : 화면의 너비, 높이를 조정할 수 있습니다. "top right bottom left" 형태로 기재하며 반드시 단위를 명시해야합니다.
+
+## 반환값
+
+`ref`: focus될 DOM요소에 할당해줄 ref 객체입니다.
+
+<Canvas of={Focus.defaultStory} />

src/stories/useFocus/Focus.css.ts

@@ -0,0 +1,17 @@
+import { style } from '@vanilla-extract/css';
+
+export const backgroundDiv = style({
+  height: 100,
+});
+
+export const scrollDiv = style({
+  position: 'absolute',
+  backgroundColor: 'black',
+  color: 'white',
+  borderRadius: 10,
+  alignItems: 'center',
+  justifyContent: 'center',
+  display: 'flex',
+  padding: 16,
+  top: 200,
+});

src/stories/useFocus/Focus.stories.ts

@@ -0,0 +1,21 @@
+import { Meta, StoryObj } from '@storybook/react';
+import Focus from './Focus';
+
+const meta = {
+  title: 'hooks/useFocus',
+  component: Focus,
+  parameters: {
+    layout: 'centered',
+    docs: {
+      canvas: {},
+    },
+  },
+} satisfies Meta<typeof Focus>;
+
+export default meta;
+
+type Story = StoryObj<typeof meta>;
+
+export const defaultStory: Story = {
+  args: {},
+};

src/stories/useFocus/Focus.tsx

@@ -0,0 +1,16 @@
+import React, { useState } from 'react';
+import useFocus from '@/useFocus/useFocus';
+import { backgroundDiv, scrollDiv } from './Focus.css';
+
+export default function Focus() {
+  const [message, setMessage] = useState('NOT FOCUS');
+  const ref = useFocus<HTMLDivElement>(() => setMessage('FOCUS!'), 1, '-10px');
+
+  return (
+    <div className={backgroundDiv}>
+      <div ref={ref} className={scrollDiv}>
+        {message}
+      </div>
+    </div>
+  );
+}

src/useFocus/useFocus.test.tsx

@@ -0,0 +1,57 @@
+import { fireEvent, render } from '@testing-library/react';
+import useFocus from './useFocus';
+import React from 'react';
+
+interface Entrie {
+  target: Element;
+  isIntersecting: boolean;
+}
+
+const mockIntersectionObserver = class {
+  entries: Entrie[];
+  constructor(callback) {
+    this.entries = [];
+    window.addEventListener('scroll', () => {
+      if (window.scrollY > 50) {
+        this.entries.map((entry) => {
+          entry.isIntersecting = this.isInViewPort();
+        });
+      }
+      callback(this.entries, this);
+    });
+  }
+
+  isInViewPort() {
+    return true;
+  }
+
+  observe(target: Element) {
+    this.entries.push({ isIntersecting: false, target });
+  }
+
+  unobserve(target) {
+    this.entries = this.entries.filter((ob) => ob.target !== target);
+  }
+
+  disconnect() {
+    this.entries = [];
+  }
+};
+
+describe('useFocus 기능 테스트', () => {
+  beforeEach(() => {
+    // eslint-disable-next-line
+    global.IntersectionObserver = mockIntersectionObserver as any;
+  });
+
+  it('focus되었을때 onFocusCallback을 실행시킬 수 있다.', async () => {
+    const mock = jest.fn();
+    const Test = () => {
+      const ref = useFocus<HTMLDivElement>(mock);
+      return <div ref={ref}>Test</div>;
+    };
+    render(<Test />);
+    fireEvent.scroll(window, { target: { scrollY: 100 } });
+    expect(mock).toHaveBeenCalled();
+  });
+});

src/useFocus/useFocus.ts

@@ -0,0 +1,36 @@
+import { useCallback, useEffect, useRef } from 'react';
+
+export default function useFocus<T extends HTMLElement>(
+  onFocusCallback: (() => void) | (() => Promise<void>),
+  threshold = 0.1,
+  rootMargin?: string,
+) {
+  const elementRef = useRef<T>(null);
+
+  const handleScroll: IntersectionObserverCallback = useCallback(([entry]) => {
+    const { current } = elementRef;
+    if (current) {
+      if (entry.isIntersecting) {
+        onFocusCallback();
+      }
+    }
+  }, []);
+
+  useEffect(() => {
+    let observer: IntersectionObserver;
+    const { current } = elementRef;
+
+    if (current) {
+      observer = new IntersectionObserver(handleScroll, {
+        threshold,
+        rootMargin: rootMargin || '0px 0px 0px 0px',
+      });
+
+      observer.observe(current);
+
+      return () => observer && observer.disconnect();
+    }
+  }, [handleScroll]);
+
+  return elementRef;
+}