Add u8aToHex (#73)

* Add u8aToHex

* Update doc

* Cleanup allocation

* Fix typo

packages/util/docs/u8a.md

@@ -7,6 +7,7 @@ Utility methods to convert to and from `Uint8Array` objects
 - [u8aFromString](#u8afromstring) Creates a Uint8Array object from a string.
 - [u8aFromUtf8](#u8afromutf8) Creates a Uint8Array object from a utf-8 string.
 - [u8aToBuffer](#u8atobuffer) Creates a Buffer object from a hex string.
+- [u8aToHex](#u8atohex) Creates a hex string from a Uint8Array object.
 - [u8aToUtf8](#u8atoutf8) Creates a utf-8 string from a Uint8Array object.
 
 ## u8aFromBuffer
@@ -84,6 +85,23 @@ import { u8aToBuffer } from '@polkadot/util';
 console.log('Buffer', u8aToBuffer('0x123480001f'));
 ```
 
+## u8aToHex
+
+Creates a hex string from a Uint8Array object. 
+
+```js
+u8aToHex (value?: UInt8Array): string
+```
+
+
+`UInt8Array` input values return the actual hex string. `null` or `undefined` values returns an `0x` string.
+
+```js
+import { u8aToHex\ } from '@polkadot/util';
+
+u8aToHex(new Uint8Array([0x68, 0x65, 0x6c, 0x6c, 0xf])); // 0x68656c0f
+```
+
 ## u8aToUtf8
 
 Creates a utf-8 string from a Uint8Array object. 
@@ -96,7 +114,7 @@ u8aToUtf8 (value?: UInt8Array): string
 `UInt8Array` input values return the actual decoded utf-8 string. `null` or `undefined` values returns an empty string.
 
 ```js
-import { u8aToString } from '@polkadot/util';
+import { u8aToUtf8 } from '@polkadot/util';
 
 u8aToUtf8(new Uint8Array([0x68, 0x65, 0x6c, 0x6c, 0x6f])); // hello
 ```

packages/util/src/u8a/index.js

@@ -8,6 +8,7 @@ const u8aFromHex = require('./fromHex');
 const u8aFromUtf8 = require('./fromUtf8');
 const u8aFromString = require('./fromString');
 const u8aToBuffer = require('./toBuffer');
+const u8aToHex = require('./toHex');
 const u8aToUtf8 = require('./toUtf8');
 
 /**
@@ -19,5 +20,6 @@ module.exports = {
   u8aFromString,
   u8aFromUtf8,
   u8aToBuffer,
+  u8aToHex,
   u8aToUtf8
 };

packages/util/src/u8a/toHex.js

@@ -0,0 +1,25 @@
+// Copyright 2017-2018 Jaco Greeff
+// This software may be modified and distributed under the terms
+// of the ISC license. See the LICENSE file for details.
+// @flow
+
+/**
+  @name u8aToHex
+  @signature u8aToHex (value?: UInt8Array): string
+  @summary Creates a hex string from a Uint8Array object.
+  @description
+    `UInt8Array` input values return the actual hex string. `null` or `undefined` values returns an `0x` string.
+  @example
+    import { u8aToHex } from '@polkadot/util';
+
+    u8aToHex(new Uint8Array([0x68, 0x65, 0x6c, 0x6c, 0xf])); // 0x68656c0f
+*/
+module.exports = function u8aToHex (value?: Uint8Array): string {
+  if (!value || !value.length) {
+    return '0x';
+  }
+
+  return value.reduce((result, item) => {
+    return result + ('0' + item.toString(16)).slice(-2);
+  }, '0x');
+};

packages/util/src/u8a/toHex.spec.js

@@ -0,0 +1,21 @@
+// Copyright 2017-2018 Jaco Greeff
+// This software may be modified and distributed under the terms
+// of the ISC license. See the LICENSE file for details.
+
+const { u8aToHex } = require('./index');
+
+describe('u8aToHex', () => {
+  it('returns empty as 0x', () => {
+    expect(
+      u8aToHex()
+    ).toEqual('0x');
+  });
+
+  it('returns the hex value for the array', () => {
+    expect(
+      u8aToHex(
+        new Uint8Array([128, 0, 10])
+      )
+    ).toEqual('0x80000a');
+  });
+});

packages/util/src/u8a/toUtf8.js

@@ -14,7 +14,7 @@ const decoder = new TextDecoder('utf-8');
   @description
     `UInt8Array` input values return the actual decoded utf-8 string. `null` or `undefined` values returns an empty string.
   @example
-    import { u8aToString } from '@polkadot/util';
+    import { u8aToUtf8 } from '@polkadot/util';
 
     u8aToUtf8(new Uint8Array([0x68, 0x65, 0x6c, 0x6c, 0x6f])); // hello
 */