Give a proper warning if improper arguments are passed

__tests__/index.js

@@ -8,6 +8,29 @@ describe('markdown-to-jsx', () => {
 
     afterEach(() => ReactDOM.unmountComponentAtNode(mountNode));
 
+    it('should throw if not passed a string (first arg)', () => {
+        expect(() => converter('')).not.toThrow();
+
+        expect(() => converter()).toThrow();
+        expect(() => converter(1)).toThrow();
+        expect(() => converter(function(){})).toThrow();
+        expect(() => converter({})).toThrow();
+        expect(() => converter([])).toThrow();
+        expect(() => converter(null)).toThrow();
+        expect(() => converter(true)).toThrow();
+    });
+
+    it('should throw if not passed an object or undefined (second arg)', () => {
+        expect(() => converter('')).not.toThrow();
+        expect(() => converter('', {})).not.toThrow();
+
+        expect(() => converter('', 1)).toThrow();
+        expect(() => converter('', function(){})).toThrow();
+        expect(() => converter('', [])).toThrow();
+        expect(() => converter('', null)).toThrow();
+        expect(() => converter('', true)).toThrow();
+    });
+
     it('should handle a basic string', () => {
         const element = render(converter('Hello.'));
         const elementNode = ReactDOM.findDOMNode(element);

index.js

@@ -293,6 +293,17 @@ function extractDefinitionsFromASTTree(ast) {
 export default function markdownToJSX(markdown, remarkOptions = {}) {
     let ast;
 
+    if (typeof markdown !== 'string') {
+        throw new Error(`markdown-to-jsx: the first argument must be
+                         a string`);
+    }
+
+    if (Object.prototype.toString.call(remarkOptions) !== '[object Object]') {
+        throw new Error(`markdown-to-jsx: the second argument must be
+                         undefined or an object literal ({}) containing
+                         valid remark options`);
+    }
+
     remarkOptions.position = remarkOptions.position || false;
     remarkOptions.footnotes = remarkOptions.footnotes || true;