ecmascript-2017

问题 I have two async functions. Both of them are waiting for two 3 seconds function calls. But the second one is faster than the first. I think the faster one is running in parallel and other in serial. Is my assumption correct? If yes, why is this happening as both the functions look logically same? function sleep() { return new Promise(resolve => { setTimeout(resolve, 3000); }); } async function serial() { await sleep(); await sleep(); } async function parallel() { var a = sleep(); var b =

问题 My function resolves a promise that resolves as soon as the http server starts. This is my code: function start() { return new Promise((resolve, reject) { this.server = Http.createServer(app); this.server.listen(port, () => { resolve(); }); }) } How do i convert the start function to async/await? 回答1: Include async before the function declaration and await the Promise constructor. Though note, you would essentially be adding code to the existing pattern. await converts a value to a Promise ,

问题 I'm trying to learn async-await. In this code - const myFun = () => { let state = false; setTimeout(() => {state = true}, 2000); return new Promise((resolve, reject) => { setTimeout(() => { if(state) { resolve('State is true'); } else { reject('State is false'); } }, 3000); }); } const getResult = async () => { return await myFun(); } console.log(getResult()); why am I getting output as - Promise { <pending> } Instead of some value? Shouldn't the getResult() function wait for myFun() function

问题 This proposal suggests that async functions can use generator functions under the hood, although I cannot find a confirmation of this in ES2017 spec. Moreover, when generator prototype becomes messed up in Chrome/Node.js, async functions don't seem to be affected, this suggests that GeneratorFunction isn't used by AsyncFunction , at least directly: Object.getPrototypeOf((function * () {}).prototype).next = null; (async () => { return await Promise.resolve(1); })() .then(console.log); How

问题 I'm trying async/await functionality. I have such code imitating a request: const getJSON = async () => { const request = () => new Promise((resolve, reject) => ( setTimeout(() => resolve({ foo: 'bar'}), 2000) )); const json = await request(); return json; } When I use the code in this way console.log(getJSON()); // returns Promise it returns a Promise but when I call this line of code getJSON().then(json => console.log(json)); // prints { foo: 'bar' } it prints json as expected Is it

问题 I'm trying async/await functionality. I have such code imitating a request: const getJSON = async () => { const request = () => new Promise((resolve, reject) => ( setTimeout(() => resolve({ foo: 'bar'}), 2000) )); const json = await request(); return json; } When I use the code in this way console.log(getJSON()); // returns Promise it returns a Promise but when I call this line of code getJSON().then(json => console.log(json)); // prints { foo: 'bar' } it prints json as expected Is it

问题 In https://stackoverflow.com/a/18658613/779159 is an example of how to calculate the md5 of a file using the built-in crypto library and streams. var fs = require('fs'); var crypto = require('crypto'); // the file you want to get the hash var fd = fs.createReadStream('/some/file/name.txt'); var hash = crypto.createHash('sha1'); hash.setEncoding('hex'); fd.on('end', function() { hash.end(); console.log(hash.read()); // the desired sha1sum }); // read all file and pipe it (write it) to the hash

问题 So i'm using express.js and looking into using async/await with node 7. Is there a way that I can still catch errors but get rid of the try/catch block? Perhaps a function wrapper? I'm not sure how this would actually execute the function's code and also call next(err) . exports.index = async function(req, res, next) { try { let user = await User.findOne().exec(); res.status(200).json(user); } catch(err) { next(err); } } Something like this...? function example() { // Implements try/catch

问题 When using a simple callback such as in the example below: test() { api.on( 'someEvent', function( response ) { return response; }); } How can the function be changed to use async / await? Specifically, assuming 'someEvent' is guaranteed to be called once and only once, I'd like the function test to be an async function which does not return until the callback is executed such as: async test() { return await api.on( 'someEvent' ); } 回答1: async/await is not magic. An async function is a

问题 I'm using await within an async function execute functions in a particular order, if you see here - I wanted startAnim to wait until hideMoveUI had finished executing to execute itself. Though my console log returns: startAnim hideMoveUI My code: async function printAll() { await hideMoveUI(); await startAnim(); } printAll(); hideMoveUI = () => { setTimeout(() => { console.log('hideMoveUI'); }, 3000); } startAnim =() => { setTimeout(() => { console.log('startAnim'); }, 500); } Is setTimeout