init

src/index.ts

@@ -1,5 +1 @@
-
-
-export { default as power } from "./sample"
-
-export { default as sqrt } from "./sample2"
+export { default as useCountdown } from './useCountdown';

src/sample.ts

@@ -1,11 +0,0 @@
-const power = (n? : number) : number | undefined => {
-    if( typeof n === "undefined" || n === null){
-        return  undefined
-    }
-    if(typeof n !== "number"){
-        return undefined
-    }
-    return Math.pow(n, 2)
-}
-
-export default power

src/sample2.ts

@@ -1,11 +0,0 @@
-const sqrt = (n : number): number | undefined => {
-    if( typeof n === "undefined" || n === null){
-        return  undefined
-    }
-    if(typeof n !== "number"){
-        return undefined
-    }
-    return Math.sqrt(n)
-}
-
-export default sqrt

src/useCountdown.ts

@@ -0,0 +1,65 @@
+import React from 'react';
+import Timeout = NodeJS.Timeout;
+
+interface useCountdownOptions {
+    now?: () => Date;
+    onEnd?: () => void;
+    onCount?: (timeLeft: number) => void;
+    step?: number; // Millisecond
+}
+
+interface CountdownHookResult {
+    timeleft: number;
+    start: (timeLeft: number) => void;
+}
+
+const DEFAULT_OPTIONS: useCountdownOptions = {
+    step: 1000,
+};
+
+function useCountdown(options?: useCountdownOptions): CountdownHookResult {
+    const [timeleft, setTimeleft] = React.useState<number | undefined>();
+
+    const [targetDatetime, setTargetDatetime] = React.useState<Date>();
+
+    const { step, onCount, onEnd } = {
+        ...DEFAULT_OPTIONS,
+        ...options,
+    };
+
+    const start = (countAsM: number) => {
+        setTimeleft(countAsM);
+    };
+    let varTimeout: number | null = null;
+
+    React.useEffect(() => {
+        return () => clearTimeout(varTimeout!);
+    }, []);
+
+    React.useEffect(() => {
+        if (timeleft === undefined) {
+            return;
+        }
+
+        const newTimeleft = timeleft - step!;
+
+        if (newTimeleft < 0) {
+            setTimeleft(0);
+            onEnd?.();
+        } else {
+            onCount?.(timeleft);
+            varTimeout = setTimeout(() => {
+                setTimeleft(newTimeleft);
+            }, step);
+        }
+    }, [timeleft]);
+
+    const result: CountdownHookResult = {
+        timeleft: timeleft || 0,
+        start,
+    };
+
+    return result;
+}
+
+export default useCountdown;