Support error instance

README.md

@@ -3,7 +3,7 @@
 You can't use `throw` statement in expressions in JavaScript:
 
 ```js
-arg = arg || throw new Error('arg is required'); 
+arg = arg || throw new Error('arg is required');
 // => SyntaxError: Unexpected token throw
 ```
 
@@ -14,13 +14,19 @@ var thr = require('throw');
 
 // ...
 
-arg = arg || thr('arg is required'); 
+arg = arg || thr('arg is required');
 ```
 
 Messages can contain `printf`-like placeholders:
 
 ```js
-arg = arg || thr('"%s" is required', argName); 
+arg = arg || thr('"%s" is required', argName);
+```
+
+You can specify instance of `Error` instead of message:
+
+```js
+arg = arg || thr(new Error('arg is required'));
 ```
 
 ## Installation

index.js

@@ -3,9 +3,13 @@ var format = require('util').format;
 /**
  * Function wrapper for throw statement.
  * Throw an error with formatted message.
- * @param {String} errorMessage
+ * @param {Error|String} error — instance of error or error message.
  * @throws
  */
-module.exports = function(errorMessage) {
+module.exports = function(error) {
+    if (error instanceof Error) {
+        throw error;
+    }
+
     throw new Error(format.apply(null, arguments));
 };