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Merge pull request #283 from jquintozamora/master
Async Await Support in TypeScript and samples
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‎code/async-await/es5/asyncAwaitES5.js

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var __awaiter = (this && this.__awaiter) || function (thisArg, _arguments, P, generator) {
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return new (P || (P = Promise))(function (resolve, reject) {
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function fulfilled(value) { try { step(generator.next(value)); } catch (e) { reject(e); } }
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function rejected(value) { try { step(generator["throw"](value)); } catch (e) { reject(e); } }
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function step(result) { result.done ? resolve(result.value) : new P(function (resolve) { resolve(result.value); }).then(fulfilled, rejected); }
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step((generator = generator.apply(thisArg, _arguments || [])).next());
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});
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};
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var __generator = (this && this.__generator) || function (thisArg, body) {
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var _ = { label: 0, sent: function() { if (t[0] & 1) throw t[1]; return t[1]; }, trys: [], ops: [] }, f, y, t, g;
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return g = { next: verb(0), "throw": verb(1), "return": verb(2) }, typeof Symbol === "function" && (g[Symbol.iterator] = function() { return this; }), g;
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function verb(n) { return function (v) { return step([n, v]); }; }
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function step(op) {
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if (f) throw new TypeError("Generator is already executing.");
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while (_) try {
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if (f = 1, y && (t = y[op[0] & 2 ? "return" : op[0] ? "throw" : "next"]) && !(t = t.call(y, op[1])).done) return t;
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if (y = 0, t) op = [0, t.value];
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switch (op[0]) {
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case 0: case 1: t = op; break;
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case 4: _.label++; return { value: op[1], done: false };
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case 5: _.label++; y = op[1]; op = [0]; continue;
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case 7: op = _.ops.pop(); _.trys.pop(); continue;
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default:
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if (!(t = _.trys, t = t.length > 0 && t[t.length - 1]) && (op[0] === 6 || op[0] === 2)) { _ = 0; continue; }
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if (op[0] === 3 && (!t || (op[1] > t[0] && op[1] < t[3]))) { _.label = op[1]; break; }
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if (op[0] === 6 && _.label < t[1]) { _.label = t[1]; t = op; break; }
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if (t && _.label < t[2]) { _.label = t[2]; _.ops.push(op); break; }
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if (t[2]) _.ops.pop();
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_.trys.pop(); continue;
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}
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op = body.call(thisArg, _);
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} catch (e) { op = [6, e]; y = 0; } finally { f = t = 0; }
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if (op[0] & 5) throw op[1]; return { value: op[0] ? op[1] : void 0, done: true };
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}
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};
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function delay(milliseconds, count) {
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return new Promise(function (resolve) {
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setTimeout(function () {
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resolve(count);
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}, milliseconds);
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});
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}
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// async function allways return a Promise
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function dramaticWelcome() {
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return __awaiter(this, void 0, void 0, function () {
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var i, count;
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return __generator(this, function (_a) {
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switch (_a.label) {
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case 0:
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console.log("Hello");
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i = 0;
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_a.label = 1;
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case 1:
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if (!(i < 5)) return [3 /*break*/, 4];
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return [4 /*yield*/, delay(500, i)];
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case 2:
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count = _a.sent();
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console.log(count);
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_a.label = 3;
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case 3:
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i++;
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return [3 /*break*/, 1];
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case 4:
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console.log("World!");
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return [2 /*return*/];
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}
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});
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});
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}
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dramaticWelcome();

‎code/async-await/es5/asyncAwaitES5.ts

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function delay(milliseconds: number, count: number): Promise<number> {
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return new Promise<number>(resolve => {
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setTimeout(() => {
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resolve(count);
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}, milliseconds);
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});
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}
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// async function allways return a Promise
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async function dramaticWelcome(): Promise<void> {
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console.log("Hello");
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for (let i = 0; i < 5; i++) {
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// await is converting Promise<number> into number
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const count:number = await delay(500, i);
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console.log(count);
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}
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console.log("World!");
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}
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dramaticWelcome();

‎code/async-await/es5/tsconfig.json

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{
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"compilerOptions": {
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"target": "es5", /* Specify ECMAScript target version: 'ES3' (default), 'ES5', 'ES2015', 'ES2016', 'ES2017', or 'ESNEXT'. */
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"module": "commonjs", /* Specify module code generation: 'commonjs', 'amd', 'system', 'umd' or 'es2015'. */
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"lib": ["dom", "es2015.promise", "es5"] /* Specify library files to be included in the compilation: */
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},
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"files": [
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"./asyncAwaitES5.ts"
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]
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}

‎code/async-await/es6/asyncAwaitES6.js

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var __awaiter = (this && this.__awaiter) || function (thisArg, _arguments, P, generator) {
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return new (P || (P = Promise))(function (resolve, reject) {
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function fulfilled(value) { try { step(generator.next(value)); } catch (e) { reject(e); } }
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function rejected(value) { try { step(generator["throw"](value)); } catch (e) { reject(e); } }
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function step(result) { result.done ? resolve(result.value) : new P(function (resolve) { resolve(result.value); }).then(fulfilled, rejected); }
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step((generator = generator.apply(thisArg, _arguments || [])).next());
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});
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};
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function delay(milliseconds, count) {
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return new Promise(resolve => {
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setTimeout(() => {
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resolve(count);
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}, milliseconds);
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});
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}
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// async function allways return a Promise
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function dramaticWelcome() {
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return __awaiter(this, void 0, void 0, function* () {
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console.log("Hello");
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for (let i = 0; i < 5; i++) {
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// await is converting Promise<number> into number
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const count = yield delay(500, i);
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console.log(count);
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}
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console.log("World!");
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});
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}
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dramaticWelcome();

‎code/async-await/es6/asyncAwaitES6.ts

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function delay(milliseconds: number, count: number): Promise<number> {
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return new Promise<number>(resolve => {
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setTimeout(() => {
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resolve(count);
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}, milliseconds);
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});
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}
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// async function allways return a Promise
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async function dramaticWelcome(): Promise<void> {
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console.log("Hello");
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for (let i = 0; i < 5; i++) {
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// await is converting Promise<number> into number
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const count:number = await delay(500, i);
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console.log(count);
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}
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console.log("World!");
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}
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dramaticWelcome();

‎code/async-await/es6/tsconfig.json

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{
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"compilerOptions": {
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"target": "es6", /* Specify ECMAScript target version: 'ES3' (default), 'ES5', 'ES2015', 'ES2016', 'ES2017', or 'ESNEXT'. */
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"module": "commonjs" /* Specify module code generation: 'commonjs', 'amd', 'system', 'umd' or 'es2015'. */
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},
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"files": [
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"./asyncAwaitES6.ts"
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]
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}

‎docs/async-await.md

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where the `wrapToReturnPromise` just executes the generator function to get the `generator` and then use `generator.next()`, if the value is a `promise` it would `then`+`catch` the promise and depending upon the result call `generator.next(result)` or `generator.throw(error)`. That's it!
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### Async Await Support in TypeScript
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**Async - Await** has been supported by [TypeScript since version 1.7](https://www.typescriptlang.org/docs/handbook/release-notes/typescript-1-7.html). Asynchronous functions are prefixed with the *async* keyword; *await* suspends the execution until an asynchronous function return promise is fulfilled and unwraps the value from the *Promise* returned.
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It was only supported for **target es6** transpiling directly to **ES6 generators**.
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**TypeScript 2.1** [added the capability to ES3 and ES5 run-times](https://www.typescriptlang.org/docs/handbook/release-notes/typescript-2-1.html), meaning you’ll be free to take advantage of it no matter what environment you’re using. It's important to notice that we can use async / await with TypeScript 2.1 and many browsers are supported, of course, having globally added a **polyfill for Promise**.
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Let's see this **example** and take a look to this code to figure out TypeScript async / await **notation** works:
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```ts
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function delay(milliseconds: number, count: number): Promise<number> {
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return new Promise<number>(resolve => {
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setTimeout(() => {
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resolve(count);
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}, milliseconds);
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});
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}
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// async function allways return a Promise
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async function dramaticWelcome(): Promise<void> {
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console.log("Hello");
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for (let i = 0; i < 5; i++) {
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// await is converting Promise<number> into number
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const count:number = await delay(500, i);
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console.log(count);
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}
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console.log("World!");
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}
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dramaticWelcome();
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```
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**Transpiling to ES6 (--target es6)**
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```js
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var __awaiter = (this && this.__awaiter) || function (thisArg, _arguments, P, generator) {
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return new (P || (P = Promise))(function (resolve, reject) {
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function fulfilled(value) { try { step(generator.next(value)); } catch (e) { reject(e); } }
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function rejected(value) { try { step(generator["throw"](value)); } catch (e) { reject(e); } }
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function step(result) { result.done ? resolve(result.value) : new P(function (resolve) { resolve(result.value); }).then(fulfilled, rejected); }
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step((generator = generator.apply(thisArg, _arguments || [])).next());
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});
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};
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function delay(milliseconds, count) {
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return new Promise(resolve => {
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setTimeout(() => {
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resolve(count);
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}, milliseconds);
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});
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}
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// async function allways return a Promise
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function dramaticWelcome() {
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return __awaiter(this, void 0, void 0, function* () {
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console.log("Hello");
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for (let i = 0; i < 5; i++) {
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// await is converting Promise<number> into number
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const count = yield delay(500, i);
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console.log(count);
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}
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console.log("World!");
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});
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}
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dramaticWelcome();
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```
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You can see full example [here][asyncawaites6code].
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**Transpiling to ES5 (--target es5)**
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```js
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var __awaiter = (this && this.__awaiter) || function (thisArg, _arguments, P, generator) {
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return new (P || (P = Promise))(function (resolve, reject) {
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function fulfilled(value) { try { step(generator.next(value)); } catch (e) { reject(e); } }
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function rejected(value) { try { step(generator["throw"](value)); } catch (e) { reject(e); } }
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function step(result) { result.done ? resolve(result.value) : new P(function (resolve) { resolve(result.value); }).then(fulfilled, rejected); }
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step((generator = generator.apply(thisArg, _arguments || [])).next());
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});
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};
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var __generator = (this && this.__generator) || function (thisArg, body) {
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var _ = { label: 0, sent: function() { if (t[0] & 1) throw t[1]; return t[1]; }, trys: [], ops: [] }, f, y, t, g;
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return g = { next: verb(0), "throw": verb(1), "return": verb(2) }, typeof Symbol === "function" && (g[Symbol.iterator] = function() { return this; }), g;
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function verb(n) { return function (v) { return step([n, v]); }; }
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function step(op) {
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if (f) throw new TypeError("Generator is already executing.");
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while (_) try {
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if (f = 1, y && (t = y[op[0] & 2 ? "return" : op[0] ? "throw" : "next"]) && !(t = t.call(y, op[1])).done) return t;
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if (y = 0, t) op = [0, t.value];
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switch (op[0]) {
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case 0: case 1: t = op; break;
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case 4: _.label++; return { value: op[1], done: false };
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case 5: _.label++; y = op[1]; op = [0]; continue;
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case 7: op = _.ops.pop(); _.trys.pop(); continue;
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default:
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if (!(t = _.trys, t = t.length > 0 && t[t.length - 1]) && (op[0] === 6 || op[0] === 2)) { _ = 0; continue; }
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if (op[0] === 3 && (!t || (op[1] > t[0] && op[1] < t[3]))) { _.label = op[1]; break; }
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if (op[0] === 6 && _.label < t[1]) { _.label = t[1]; t = op; break; }
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if (t && _.label < t[2]) { _.label = t[2]; _.ops.push(op); break; }
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if (t[2]) _.ops.pop();
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_.trys.pop(); continue;
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}
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op = body.call(thisArg, _);
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} catch (e) { op = [6, e]; y = 0; } finally { f = t = 0; }
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if (op[0] & 5) throw op[1]; return { value: op[0] ? op[1] : void 0, done: true };
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}
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};
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function delay(milliseconds, count) {
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return new Promise(function (resolve) {
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setTimeout(function () {
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resolve(count);
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}, milliseconds);
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});
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}
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// async function allways return a Promise
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function dramaticWelcome() {
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return __awaiter(this, void 0, void 0, function () {
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var i, count;
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return __generator(this, function (_a) {
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switch (_a.label) {
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case 0:
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console.log("Hello");
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i = 0;
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_a.label = 1;
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case 1:
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if (!(i < 5)) return [3 /*break*/, 4];
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return [4 /*yield*/, delay(500, i)];
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case 2:
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count = _a.sent();
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console.log(count);
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_a.label = 3;
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case 3:
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i++;
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return [3 /*break*/, 1];
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case 4:
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console.log("World!");
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return [2 /*return*/];
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}
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});
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});
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}
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dramaticWelcome();
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```
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You can see full example [here][asyncawaites5code].
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**Note**: for both target scenarios, we need to make sure our run-time has an ECMAScript-compliant Promise available globally. That might involve grabbing a polyfill for Promise. We also need to make sure that TypeScript knows Promise exists by setting your lib flag to something like "dom", "es2015" or "dom", "es2015.promise", "es5".
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**We can see what browsers DO have Promise support (native and polyfilled) [here](https://kangax.github.io/compat-table/es6/#test-Promise).**
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[generators]:./generators.md
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[asyncawaites5code]:../code/async-await/es5/asyncAwaitES5.js
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[asyncawaites6code]:../code/async-await/es6/asyncAwaitES6.js

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