add solution

Author: Neil94n

solution/0028.Implement strStr()/Solution.js

@@ -0,0 +1,22 @@
+/**
+ * @param {string} haystack
+ * @param {string} needle
+ * @return {number}
+ */
+var strStr = function (haystack, needle) {
+    const slen = haystack.length
+    const plen = needle.length
+    if (slen == plen) {
+        return haystack == needle ? 0 : -1
+    }
+    for (let i = 0; i <= slen - plen; i++) {
+        let j
+        for (j = 0; j < plen; j++) {
+            if (haystack[i + j] != needle[j]) {
+                break
+            }
+        }
+        if (j == plen) return i
+    }
+    return -1
+};