added is optional feature and fixed res sent even after no error issue, updated readme.md

Author: jithilprakash

example/index.js

@@ -6,7 +6,7 @@ const { validate } = require("../index");
 let valuedValidate = validate(require("./rules"));
 
 
-app.get("/checkFromQuery/:id", valuedValidate, (req, res) => {
+app.get("/checkFromQuery", valuedValidate, (req, res) => {
     res.send("hey you get all inputs correct");
 });
 

example/rules.js

@@ -2,7 +2,8 @@ module.exports = [
     {
         "from": "query",
         "key": "emailId",
-        validation_function: value => value.indexOf("@") > -1
+        validation_function: value => value.indexOf("@") > -1,
+        is_optional: true
     },
     {
         "from": "header",

index.js

@@ -1,29 +1,35 @@
 const { extractValue, dataTypeCheck } = require("./utils");
 
-const validate = (rules) => {
-    return (req, res, next) => {
-        let error_messages = [];
-        rules.forEach(rule => {
-            let value = extractValue(req, rule);
-            if (!value) {
-                error_messages.push(rule.message || `Invalid ${rule.key}, value not found in ${rule.from}`);
-                return;
-            }
-            if (rule.datatype && !dataTypeCheck(rule.datatype, value)) {
-                error_messages.push(rule.message || `Invalid ${rule.key}, required a ${rule.datatype} value`);
-                return;
-            }
-            if (rule.validation_function && !rule.validation_function(value)) {
-                error_messages.push(rule.message || `Invalid ${rule.key}`);
-            }
-        });
-        if (error_messages) {
-            res.status(400);
-            res.send({ error_messages });
-        } else {
-            next();
-        }
+const validate = rules => {
+  return (req, res, next) => {
+    let error_messages = [];
+    rules.forEach(rule => {
+      let value = extractValue(req, rule);
+      if (rule.is_optional && !value) {
+        return;
+      }
+      if (!value) {
+        error_messages.push(rule.message || `Invalid ${rule.key}, value not found in ${rule.from}`);
+        return;
+      }
+      if (rule.datatype && !dataTypeCheck(rule.datatype, value)) {
+        error_messages.push(
+          rule.message ||
+            `Invalid ${rule.key}, required a ${rule.datatype} value`
+        );
+        return;
+      }
+      if (rule.validation_function && !rule.validation_function(value)) {
+        error_messages.push(rule.message || `Invalid ${rule.key}`);
+      }
+    });
+    if (error_messages.length > 0) {
+      res.status(400);
+      res.send({ error_messages });
+    } else {
+      next();
     }
-}
+  };
+};
 
-exports.validate = validate;
+exports.validate = validate;