Update JS API and publish 0.2.0 (#210)

Author: tomaka

bin/wasm-node/javascript/README.md

@@ -0,0 +1,33 @@
+# Light client for Polkadot and Substrate-based chains
+
+This JavaScript library provides a light client for
+[the Polkadot blockchain](https://polkadot.network/) and for chains built using
+[the Substrate blockchain framework](https://substrate.dev/).
+
+It is an "actual" light client, in the sense that it is byzantine-resilient.
+It does rely on the presence of an RPC server, but directly connects to the
+full nodes of the network.
+
+## Usage
+
+```
+import * as substrate_lite from 'substrate-lite';
+
+// Load a string chain specifications.
+const chain_spec = Buffer.from(fs.readFileSync('./westend.json')).toString('utf8');
+
+substrate_lite
+  .start({
+    chain_spec: chain_spec,
+    json_rpc_callback: (resp) => {
+        // Called whenever the client emits a response to a JSON-RPC request,
+        // or a JSON-RPC pub-sub notification.
+        console.log(resp)
+    }
+  })
+  .then((client) => {
+    client.send_json_rpc('{"jsonrpc":"2.0","id":1,"method":"system_name","params":[]}');
+  })
+```
+
+The `start` function returns a `Promise`.

bin/wasm-node/javascript/index.js

@@ -22,7 +22,13 @@ import Websocket from 'websocket';
 
 import { default as wasm_base64 } from './autogen/wasm.js';
 
-export async function start(chain_specs, json_rpc_callback) {
+export async function start(config) {
+  const chain_spec = config.chain_spec;
+  const json_rpc_callback = config.json_rpc_callback;
+
+  if (Object.prototype.toString.call(chain_spec) !== '[object String]')
+    throw 'config must include a string chain_spec';
+
   var module;
 
   // List of environment variables to feed to the Rust program. An array of strings.
@@ -222,12 +228,12 @@ export async function start(chain_specs, json_rpc_callback) {
 
   module = result.instance;
 
-  let chain_specs_len = Buffer.byteLength(chain_specs, 'utf8');
-  let chain_specs_ptr = module.exports.alloc(chain_specs_len);
+  let chain_spec_len = Buffer.byteLength(chain_spec, 'utf8');
+  let chain_spec_ptr = module.exports.alloc(chain_spec_len);
   Buffer.from(module.exports.memory.buffer)
-    .write(chain_specs, chain_specs_ptr);
+    .write(chain_spec, chain_spec_ptr);
 
-  module.exports.init(chain_specs_ptr, chain_specs_len, 0, 0);
+  module.exports.init(chain_spec_ptr, chain_spec_len, 0, 0);
 
   return {
     send_json_rpc: (request) => {

bin/wasm-node/javascript/package.json

@@ -1,6 +1,6 @@
 {
   "name": "substrate-lite",
-  "version": "0.1.3",
+  "version": "0.2.0",
   "description": "Light client that connects to Polkadot and Substrate-based blockchains",
   "author": "Parity Technologies <[email protected]>",
   "license": "GPL-3.0-or-later WITH Classpath-exception-2.0",