diff --git a/modules/openapi-generator/src/main/resources/Javascript/ApiClient.mustache b/modules/openapi-generator/src/main/resources/Javascript/ApiClient.mustache
index d618e612b33c..b402e62d1a5f 100644
--- a/modules/openapi-generator/src/main/resources/Javascript/ApiClient.mustache
+++ b/modules/openapi-generator/src/main/resources/Javascript/ApiClient.mustache
@@ -119,9 +119,28 @@
     if (param instanceof Date) {
       return param.toJSON();
     }
+    if (this.canBeJsonified(param)) {
+      return JSON.stringify(param);
+    }
     return param.toString();
   };
 
+{{#emitJSDoc}}  /**
+    * Returns a boolean indicating if the parameter could be JSON.stringified
+    * @param param The actual parameter
+    * @returns {Boolean} Flag indicating if <code>param</code> can be JSON.stringified
+    */
+{{/emitJSDoc}}  exports.prototype.canBeJsonified = function(str) {
+    if (typeof str !== 'string' && typeof str !== 'object') return false;
+    try {
+      const type = str.toString();
+      return type === '[object Object]'
+          || type === '[object Array]';
+    } catch (err) {
+      return false;
+    }
+  };
+
 {{#emitJSDoc}}
  /**
    * Builds full URL by appending the given path to the base URL and replacing path parameter place-holders with parameter values.
diff --git a/modules/openapi-generator/src/main/resources/Javascript/es6/ApiClient.mustache b/modules/openapi-generator/src/main/resources/Javascript/es6/ApiClient.mustache
index c660001f1fdc..fcb92377e19c 100644
--- a/modules/openapi-generator/src/main/resources/Javascript/es6/ApiClient.mustache
+++ b/modules/openapi-generator/src/main/resources/Javascript/es6/ApiClient.mustache
@@ -108,10 +108,29 @@ class ApiClient {
         if (param instanceof Date) {
             return param.toJSON();
         }
+        if (ApiClient.canBeJsonified(param)) {
+            return JSON.stringify(param);
+        }
 
         return param.toString();
     }
 
+    {{#emitJSDoc}}/**
+    * Returns a boolean indicating if the parameter could be JSON.stringified
+    * @param param The actual parameter
+    * @returns {Boolean} Flag indicating if <code>param</code> can be JSON.stringified
+    */{{/emitJSDoc}}
+    static canBeJsonified(str) {
+        if (typeof str !== 'string' && typeof str !== 'object') return false;
+        try {
+            const type = str.toString();
+            return type === '[object Object]'
+                || type === '[object Array]';
+        } catch (err) {
+            return false;
+        }
+    };
+
     {{#emitJSDoc}}
    /**
     * Builds full URL by appending the given path to the base URL and replacing path parameter place-holders with parameter values.
diff --git a/samples/client/petstore/javascript-es6/src/ApiClient.js b/samples/client/petstore/javascript-es6/src/ApiClient.js
index 3d081bf1877a..6fba8796f928 100644
--- a/samples/client/petstore/javascript-es6/src/ApiClient.js
+++ b/samples/client/petstore/javascript-es6/src/ApiClient.js
@@ -109,10 +109,29 @@ class ApiClient {
         if (param instanceof Date) {
             return param.toJSON();
         }
+        if (ApiClient.canBeJsonified(param)) {
+            return JSON.stringify(param);
+        }
 
         return param.toString();
     }
 
+    /**
+    * Returns a boolean indicating if the parameter could be JSON.stringified
+    * @param param The actual parameter
+    * @returns {Boolean} Flag indicating if <code>param</code> can be JSON.stringified
+    */
+    static canBeJsonified(str) {
+        if (typeof str !== 'string' && typeof str !== 'object') return false;
+        try {
+            const type = str.toString();
+            return type === '[object Object]'
+                || type === '[object Array]';
+        } catch (err) {
+            return false;
+        }
+    };
+
    /**
     * Builds full URL by appending the given path to the base URL and replacing path parameter place-holders with parameter values.
     * NOTE: query parameters are not handled here.
diff --git a/samples/client/petstore/javascript-promise-es6/src/ApiClient.js b/samples/client/petstore/javascript-promise-es6/src/ApiClient.js
index d3eb5cb7184f..1b38bc4b28eb 100644
--- a/samples/client/petstore/javascript-promise-es6/src/ApiClient.js
+++ b/samples/client/petstore/javascript-promise-es6/src/ApiClient.js
@@ -109,10 +109,29 @@ class ApiClient {
         if (param instanceof Date) {
             return param.toJSON();
         }
+        if (ApiClient.canBeJsonified(param)) {
+            return JSON.stringify(param);
+        }
 
         return param.toString();
     }
 
+    /**
+    * Returns a boolean indicating if the parameter could be JSON.stringified
+    * @param param The actual parameter
+    * @returns {Boolean} Flag indicating if <code>param</code> can be JSON.stringified
+    */
+    static canBeJsonified(str) {
+        if (typeof str !== 'string' && typeof str !== 'object') return false;
+        try {
+            const type = str.toString();
+            return type === '[object Object]'
+                || type === '[object Array]';
+        } catch (err) {
+            return false;
+        }
+    };
+
    /**
     * Builds full URL by appending the given path to the base URL and replacing path parameter place-holders with parameter values.
     * NOTE: query parameters are not handled here.