Print a deprecation warning if input is not a string, cc #486

validator.js

@@ -134,6 +134,14 @@
     };
 
     validator.toString = function (input) {
+        // The library validates strings only. Currently it coerces all input to a string, but this
+        // will go away in an upcoming major version change. Print a deprecation notice for now
+        if (typeof input !== 'string' && typeof console === 'object' && console
+                && typeof console.warn === 'function') {
+            console.warn('warning: you tried to validate a ' + typeof input + ' but this library ' +
+                '(github.com/chriso/validator.js) validates strings only. Please update your code ' +
+                'as this will be an error soon.')
+        }
         if (typeof input === 'object' && input !== null) {
             if (typeof input.toString === 'function') {
                 input = input.toString();