Cleanup hex functions (#130)

packages/util/src/hex/toU8a.js

@@ -3,6 +3,8 @@
 // of the ISC license. See the LICENSE file for details.
 // @flow
 
+const assert = require('../assert');
+const isHex = require('../is/hex');
 const hexStripPrefix = require('./stripPrefix');
 
 /**
@@ -23,6 +25,8 @@ module.exports = function hexToU8a (_value?: string, bitLength: number = -1): Ui
     return new Uint8Array([]);
   }
 
+  assert(isHex(_value), `Expected hex value to convert, found '${_value}'`);
+
   const value = hexStripPrefix(_value);
   const valLength = value.length / 2;
   const bufLength = Math.ceil(

packages/util/src/hex/toU8a.spec.js

@@ -19,19 +19,17 @@ describe('hexToU8a', () => {
     );
   });
 
-  it('returns a Uint8Array with the correct values (no prefix)', () => {
-    expect(
-      hexToU8a('80000a')
-    ).toEqual(
-      new Uint8Array([128, 0, 10])
-    );
-  });
-
   it('returns a Uint8Array with the correct values (bitLengfth)', () => {
     expect(
-      hexToU8a('80000a', 32)
+      hexToU8a('0x80000a', 32)
     ).toEqual(
       new Uint8Array([0, 128, 0, 10])
     );
   });
+
+  it('fails when non-hex value provided', () => {
+    expect(
+      () => hexToU8a('notahex')
+    ).toThrow(/hex value to convert/);
+  });
 });