fix: improve dictionary type checking

Passing a boolean value or NaN as a dictionary did not cause an error, and it should have. This
updates behavior and adds applicable tests.

Resolves: #39

index.js

@@ -77,8 +77,15 @@ class AlphanumericEncoder {
      */
     set dictionary(newDictionary) {
         // Check for empty dictionaries
-        if (newDictionary === null || newDictionary === undefined || newDictionary.length === 0) {
-            throw new RangeError('The dictionary cannot be null, undefined, or an empty string.')
+        if (
+            typeof newDictionary !== 'string' ||
+            newDictionary.length === 0 ||
+            // eslint-disable-next-line no-self-compare
+            newDictionary !== newDictionary // This verifies it wasn't passed NaN
+        ) {
+            throw new RangeError(
+                'The dictionary cannot be null, undefined, boolean, NaN, or an empty string.'
+            )
         }
 
         // Check for invalid characters. Using a regular expression, make sure only letters and numbers are allowed.

index.test.js

@@ -118,6 +118,18 @@ describe('Dictionary Validation', () => {
         }).toThrow(/undefined/)
     })
 
+    test.each([true, false])('Dictionary cannot be boolean %p', (input) => {
+        expect(() => {
+            encoder.dictionary = input
+        }).toThrow(/boolean/)
+    })
+
+    test('Dictionary cannot be NaN', () => {
+        expect(() => {
+            encoder.dictionary = NaN
+        }).toThrow(/NaN/)
+    })
+
     describe('Valid Dictionaries (no lower case)', () => {
         setupNewEncoderForTesting()