Update README.md

Author: yanglbme

solution/2700-2799/2707.Extra Characters in a String/README.md

@@ -210,6 +210,30 @@ impl Solution {
 }
 ```
 
+#### JavaScript
+
+```js
+/**
+ * @param {string} s
+ * @param {string[]} dictionary
+ * @return {number}
+ */
+var minExtraChar = function (s, dictionary) {
+    const ss = new Set(dictionary);
+    const n = s.length;
+    const f = Array(n + 1).fill(0);
+    for (let i = 1; i <= n; ++i) {
+        f[i] = f[i - 1] + 1;
+        for (let j = 0; j < i; ++j) {
+            if (ss.has(s.slice(j, i))) {
+                f[i] = Math.min(f[i], f[j]);
+            }
+        }
+    }
+    return f[n];
+};
+```
+
 <!-- tabs:end -->
 
 <!-- solution:end -->