Implement GraphQL subscription (#115)

* Implement subscription

* Add original subscription test

* Refactor implementation

* Update original subscription test to use resolver instead of rootValue

* Fix TS errors and format

* Update README

README.md

@@ -29,8 +29,7 @@ Done in 141.94s.
 
 ### Support for GraphQL spec
 
-The goal is to support the [June 2018 version of the GraphQL spec](https://facebook.github.io/graphql/June2018/). At this moment,
-the only missing feature is support for Subscriptions.
+The goal is to support the [June 2018 version of the GraphQL spec](https://facebook.github.io/graphql/June2018/).
 
 #### Differences to `graphql-js`
 
@@ -91,10 +90,19 @@ if (!isCompiledQuery(compiledQuery)) {
 #### Execute the Query
 
 ```js
-const executionResult = await compiledQuery.query();
+const executionResult = await compiledQuery.query(root, context, variables);
 console.log(executionResult);
 ```
 
+#### Subscribe to the Query
+
+```js
+const result = await compiledQuery.subscribe(root, context, variables);
+for await (const value of result) {
+  console.log(value);
+}
+```
+
 ## API
 
 ### compiledQuery = compileQuery(schema, document, operationName, compilerOptions)
@@ -112,14 +120,18 @@ Compiles the `document` AST, using an optional operationName and compiler option
     for overly expensive serializers
   - `customJSONSerializer` {boolean, default: false} - Whether to produce also a JSON serializer function using `fast-json-stringify`. The default stringifier function is `JSON.stringify`
 
-#### compiledQuery.compiled(root: any, context: any, variables: Maybe<{ [key: string]: any }>)
+#### compiledQuery.query(root: any, context: any, variables: Maybe<{ [key: string]: any }>)
 
 the compiled function that can be called with a root value, a context and the required variables.
 
+#### compiledQuery.subscribe(root: any, context: any, variables: Maybe<{ [key: string]: any }>)
+
+(available for GraphQL Subscription only) the compiled function that can be called with a root value, a context and the required variables to produce either an AsyncIterator (if successful) or an ExecutionResult (error).
+
 #### compiledQuery.stringify(value: any)
 
 the compiled function for producing a JSON string. It will be `JSON.stringify` unless `compilerOptions.customJSONSerializer` is true.
-The value argument should the return of the compiled GraphQL function.
+The value argument should be the return of the compiled GraphQL function.
 
 ## LICENSE
 

src/__tests__/execution.test.ts

@@ -2,6 +2,7 @@
  * Based on https://github.com/graphql/graphql-js/blob/master/src/execution/__tests__/execution-test.js
  */
 
+import { makeExecutableSchema } from "@graphql-tools/schema";
 import {
   DocumentNode,
   ExecutableDefinitionNode,
@@ -16,7 +17,6 @@ import {
   parse
 } from "graphql";
 import { CompiledQuery, compileQuery, isCompiledQuery } from "../execution";
-import { makeExecutableSchema } from "@graphql-tools/schema";
 
 function executeArgs(args: any) {
   const {
@@ -67,7 +67,7 @@ describe("Execute: Handles basic execution tasks", () => {
       })
     });
 
-    expect(() => executeQuery(schema)).toThrow("Must provide document");
+    expect(() => executeQuery(schema)).toThrow("Must provide document.");
   });
   test("throws if no resolve info enricher is not a function", async () => {
     const schema = new GraphQLSchema({