Update README_EN.md

added Javascript code

Author: AE-Hertz

solution/2600-2699/2666.Allow One Function Call/README_EN.md

@@ -91,6 +91,31 @@ function once<T extends (...args: any[]) => any>(
 
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+```js
+/**
+ * @param {Function} fn
+ * @return {Function}
+ */
+var once = function(fn) {
+    let called = false;
+    return function(...args){
+        if(!called){
+            called=true;
+            return fn(...args);
+        }
+        return undefined;
+    }
+};
+
+/**
+ * let fn = (a,b,c) => (a + b + c)
+ * let onceFn = once(fn)
+ *
+ * onceFn(1,2,3); // 6
+ * onceFn(2,3,6); // returns undefined without calling fn
+ */
+
+
 <!-- solution:end -->
 
 <!-- problem:end -->