added useRef, useContext examples

react_alap/mai/src/Adatlekero.js

@@ -0,0 +1,34 @@
+import React, {useState, useEffect} from "react"; 
+
+function Adatlekero(){
+    let [adatok, setAdatok] = useState(null);
+
+    useEffect(
+        () => {
+            async function lekeres() {
+                try{
+                    let response = await fetch("https://jsonplaceholder.typicode.com/posts");
+                    let data = await response.json();
+                    setAdatok(data);
+                } catch (error){
+                    console.error('Hiba történt: ', error);
+                }
+            }
+            lekeres();
+        }
+    );
+
+    if (!adatok) {
+        return <p>Adatok betöltése ...</p>;
+    }
+
+    return (
+        <ol>
+            {adatok.map((adat) => (
+                <li key={adat.id}>{adat.title}</li>
+            ))}
+        </ol>
+    )
+}
+
+export default Adatlekero;